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<article> <title>Exim 4 for Debian</title>
  <section> <title>Introduction</title>
    <para>
      If you're reading this, you have found the README.Debian
      file. This is good, thanks! Please continue reading this file in
      its entirety. It is full of important information and has been
      written with the questions in mind that keep popping up on the
      mailing lists.
    </para>
    <section> <title>How to find your way around the Documentation</title>
      <para>
        Exim comes with very extensive documentation. Here is how to
        find it.
     	<orderedlist>
	  <listitem>
	    <simpara>
	      A lot of information about Debian's Exim 4
              packaging can be found in this document.
            </simpara>
	  </listitem>
	  <listitem>
	    <simpara>
	      The packages contain a lot of Debian-specific man pages.
              Use the <command>apropos exim</command> command to get a list.
            </simpara>
	  </listitem>
	  <listitem>
	    <simpara>
	      Most files that control the default configuration are
	      documented in the exim4-config_files(5) man page, which
	      is symlinked to the file names. man &lt;filename&gt; should
	      lead you to the page.
            </simpara>
	  </listitem>
	  <listitem>
	    <para>
	      The very extensive Upstream documentation is shipped
	      <orderedlist>
	        <listitem>
		  <simpara>
		    in text form
	            (<filename>/usr/share/doc/exim4-base/spec.txt.gz</filename>)
	            with the binary packages.
		  </simpara>
		</listitem>
	        <listitem>
		  <simpara>
		    in HTML in the package
		    <filename>exim4-doc-html</filename>
		  </simpara>
		</listitem>
	        <listitem>
		  <simpara>
		    as a Texinfo file in the package
                    <filename>exim4-doc-info</filename>
		  </simpara>
		</listitem>
	      </orderedlist>
	    </para>
	  </listitem>
        </orderedlist>
      </para>
      <para>
        Please note that documentation found on the web or in other
	parts of the Debian system (such as the Debian Reference)
	might be outdated and thus give wrong advice. In doubt, the
	documentation listed above should take precedence.
      </para>
    </section>
    <section> <title>Getting Support</title>
      <para>
	For your questions and comments, there is a <ulink
	  url="http://lists.alioth.debian.org/mailman/listinfo/pkg-exim4-users">
	Debian-specific mailing	list</ulink>. Please ask Debian-specific
	questions there, and only write to the upstream exim-users mailing
	list if
	you are sure that your question is not Debian-specific. 
	Debian-specific questions are more likely to find answers on
	our pkg-exim4-users mailing list, while complex custom
	configuration issues might be more easily solved on the
	upstream exim-users mailing list because of the broader and
	more experienced audience there. You can subscribe to
	pkg-exim4-users <ulink
	  url="http://lists.alioth.debian.org/mailman/listinfo/pkg-exim4-users">
	  via the subscription web page;</ulink> you need to be
        subscribed to post.
      </para>
      <para>
        If you think that your question might be more easily answered
	if one knows a bit about your configuration, you might want to
	execute <command>reportbug --subject="none" --offline --quiet
	--severity=wishlist --body="none" --output=exim4.reportbug
	exim4-config</command> on the system in question, answer yes
        to both "include [extended] configuration" questions and include
	the contents of the exim4.reportbug file generated by this
	command with your question. Please check whether the file
	contains any confidential information before sending.
      </para>
    </section>
    <section> <title>Packaging</title>
      <para>
	Similar to the Apache2 package, Exim 4 is an entirely
	different package that does not currently offer a smooth
	upgrade path from Debian's Exim 3 packages.
      </para>
      <para>
	It is the first Exim package in Debian that can be configured
	using debconf. However, the entire configuration framework is
	extremely flexible, allowing you to get exactly the amount of
	control you need for the job at hand.
      </para>
      <section> <title>Feature Sets in the daemon packages</title>
	<para>
	  To use Exim 4, you need at least the following packages:
	  <variablelist>
	    <varlistentry>
	      <term>exim4-base</term>
	      <listitem>
		<simpara>support files for all Exim MTA (v4) packages</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term>exim4-config</term>
	      <listitem>
		<simpara>configuration for the Exim MTA (v4)</simpara>
	      </listitem>
	    </varlistentry>
	    <varlistentry>
	      <term>exim4-daemon-light</term>
	      <listitem>
		<simpara>lightweight exim MTA (v4) daemon</simpara>
	      </listitem>
	    </varlistentry>
	  </variablelist>
	</para>
	<para>
	  Just apting the metapackage <command>exim4</command> will pull
	  in the other packages per dependency. You'll get an exim daemon
	  with minimal feature set (no external lookups).
	</para>
	<para>
	  If you need more advanced features like LDAP, sqlite, PostgreSQL
	  and MySQL data lookups, SASL and SPA SMTP authentication, embedded
	  Perl interpreter, and exiscan-acl for integration of
	  virus-scanners and SpamAssassin, you can replace
	  <command>exim4-daemon-heavy</command> instead of
	  <command>exim4-daemon-light</command>. Additionally, the source
	  package offers infrastructure to build your own custom-tailored
	  exim4-daemon-custom which exactly fits your special local needs. 
	  The infrastructure to do so is already in place, see
	  debian/rules for instructions.
	</para>
      </section>
      <section> <title>How to build a custom daemon</title>
	<para>
	  The process of building a custom daemon is partially
          documented in the <filename>debian/rules</filename> file
	  in the source package. Patches for more documentation are welcome.
	</para>
      </section>
    </section>
  </section>
  <section> <title>Configuration of Exim 4 in the Debian packages</title>
    <para>
      Generally, the Debian Exim 4 packages are configured through
      debconf. You have been asked some questions on package installation,
      and your initial Exim configuration has been created from your
      answers. You can repeat the configuration process any time by invoking
      <command>dpkg-reconfigure exim4-config</command>. If you are an
      experienced Exim administrator and prefer to have your own,
      hand-crafted, non-automatic Exim configuration, you will find
      information about how to do so in
      <xref linkend="completely-different-configuration"/>.
    </para>
    <para>
      The debconf-driven configuration is mainly geared for a
      one-domain shell account machine/workstation with local delivery
      as suggested by the original upstream default configuration.
      If you configure the packages to handle more than one local
      domain, all local domains are treated identically. The domain
      part is not used for routing and filtering decisions.
    </para>
    <para>
      Despite the default configuration being extended somewhat from
      the original upstream, chances are that you'll need to
      manually change the Exim configuration with an editor if you intend to
      do something that is not covered by the debconf-driven configuration.
      It has never been the packages' intention to offer all possible
      configuration methods through debconf. The configuration files are
      there to be changed, feel free to do so if you see fit. The Debian
      Exim 4 maintainers have tried to make the configuration as flexible as
      possible so that manual intervention can be minimized.
    </para>
    <para>
      If you need to make manual changes to the Exim configuration,
      please be familiar with how Exim works. At minimum, have read this
      README file and the manpages delivered with the Debian Exim 4
      packages, and <filename>/usr/share/doc/exim4-base/spec.txt.gz</filename>
      chapters <phrase>"How Exim receives and delivers mail"</phrase> and
      <phrase>"The Exim run time configuration file"</phrase>.
      <filename>spec.txt.gz</filename> is an excellent reference.
    </para>
    <para>
      Please note that while most free-form fields in the
      debconf-driven configuration have the entered string end up
      verbatim in Exim's configuration file (and thus using more
      advanced features like host, address and domain lists is possible
      and will probably work), this is not officially supported.
      Only plain lists are supported in the debconf dialogs. You may
      use more advanced features, but they may stop working any time
      during upgrades.
    </para>
    <section> <title>The Configuration System</title>
        <section id="debconf-questions"> <title>The Debconf questions</title>
	    <para>
	      In this section, we try to document and explain the debconf
	      questions, which are themselves limited to a small screen of
	      information and might leave questions unanswered. Since you
	      can usually read this file only after having answered the 
	      questions, the process can always be repeated by invoking
	      <command>dpkg-reconfigure exim4-config.</command> 
	      <filename>/etc/exim4/update-exim4.conf.conf</filename>,
	      documented in the <command>update-exim4.conf</command>
	      manual page, is
	      a simple shell-script snippet used to store the answers
	      that you passed to debconf when initially configuring Exim.
	      You may also modify this file with an editor of your choice.
	      The package maintainer scripts can handle this and will
	      preserve your changes. 
	    </para>
	  <section> <title>General type of mail configuration</title>
              <para>
                This is the main configuration question which will
		control which of the remaining questions are
		presented to you. It also controls things like daemon
		invocation and delivery of outgoing mail.
              </para>
	      <section> <title> internet site; mail is sent and
	      received directly using SMTP</title>
	          <para>
		    This option is suitable for a standalone system
		    with full internet connectivity.
		  </para>
                  <itemizedlist>
                      <listitem>
		          <para>
			    The Exim SMTP daemon will accept messages
			    to local domains, and deliver them locally.
                          </para>
		      </listitem>
                      <listitem>
		          <para>
			    Outgoing mail will be delivered directly
			    to the mail exchange servers of the
			    recipient domain
                          </para>
		      </listitem>
		  </itemizedlist>
              </section>
	      <section> <title> mail sent by smarthost; received via
	      SMTP or fetchmail</title>
	          <para>
		    This option is suitable for a standalone client system
		    which has restricted internet connectivity, for
		    example on a residential connection where an SMTP
		    smarthost is used. Some ISPs block outgoing SMTP
		    connections to combat the spam problem, thus
		    requiring the use of their smarthosts. It is
		    generally a good idea to use the ISPs smart host
		    if one is connected with a dynamic IP address
		    since quite a few sites do not accept mail
		    directly delivered from a dial-in pool.
		  </para>
		  <para>
		    fetchmail can be used to retrieve incoming mail
		    from the ISP's POP3 or IMAP mail server and
		    deliver it to Exim via SMTP.
		  </para>
                  <itemizedlist>
                      <listitem>
		          <para>
			    The Exim SMTP daemon will accept messages
			    to local domains, and deliver them locally.
                          </para>
		      </listitem>
                      <listitem>
		          <para>
			    Outgoing mail will always be delivered to
			    the smarthost configured in exim4.
                          </para>
		      </listitem>
		  </itemizedlist>
              </section>
	      <section> <title>mail sent by smarthost; no local mail</title>
	          <para>
		    This option is suitable for a client system in a
		    computer pool which is not responsible for a local
		    e-mail domain. All locally generated e-mail is
		    sent to the smarthost without any local domains.
		  </para>
              </section>
	      <section> <title>local delivery only; not on a network</title>
	          <para>
		    This option is suitable for a standalone system
		    with no networking at all. Only messages for configured
		    local domains are accepted and delivered locally;
		    messages for all other domains are rejected:
		    ``Mailing to remote domains not supported''.
		  </para>
              </section>
	      <section> <title>no configuration at this time</title>
	          <para>
		    This option disables most of Debian's automatisms
		    and leaves exim in an unconfigured state.
		    update-exim4.conf will still copy
		    <filename>/etc/exim4/exim4.conf.template</filename>
		    or concatenate the files from
		    <filename>/etc/exim4/conf.d,</filename> and will
		    not generate any configuration control macros.
		    Unless you manually edit the configuration source,
		    this will leave Exim with a syntactically invalid
		    configuration file, thus in a state where the
		    daemon won't even start.
		  </para>
		  <para>
		    Only choose this option if you know what you're
		    doing and are prepared to create your own Exim
		    configuration.
		  </para>
		  <para>
		    dpkg-conffile handling is still in place, and you
		    will be offered updates for configuration
		    snippets, as soon as they become available.
		  </para>
              </section>
          </section>
	  <section> <title>System mail name</title>
	      <para>
	         The "mail name" is the domain name used to "qualify"
		 mail addresses without a domain name.
	      </para>
	      <para>
                 This name will also be used by other programs. It
		 should be the single, full domain name (FQDN).
	      </para>
	      <para>
                 For example, if a mail address on the local host is
		 foo@example.org, then the correct value for this
		 option would be example.org.
	      </para>
	      <para>
	        Exim, as a rule, handles only fully qualified mail
		addresses, that is, addresses with a local part, an @
		sign and a domain. If confronted with an unqualified
		address, that is, one without @ sign and without
       		domain, first thing exim does is qualify the address
		by adding the @ sign and a domain.
	      </para>
	      <para>
	        This qualification happens for all addresses exim
                encounters, be it sender, recipient or else.
              </para>
	      <para>
	        The domain name used to qualify unqualified mail addresses
		is called ``mail name'' on Debian systems and entered
                in this debconf dialog. What you enter here will end
		up in <filename>/etc/mailname,</filename> which is a
		file that might be used by other programs as well.
	      </para>
	      <para>
	        In some configuration types, the package configuration
		will offer you, at a later step, to hide this name 
		from outgoing messages by rewriting the headers.
	      </para>
          </section>
	  <section> <title>IP addresses to listen on for incoming SMTP
	  connections</title>
	      <para>
	        Please enter a semicolon-separated list of IP addresses.
	        The Exim SMTP listener daemon will listen on all IP
	        addresses listed here.
	      </para>
	      <para>
	        An empty value will cause Exim to listen for connections
	        on all available network interfaces.
	      </para>
	      <para>
	        If this system does only receive e-mail directly from
	        local services (and not from other hosts),
	        it is suggested to prohibit external connections to the
	        local Exim daemon. Such services include e-mail
                programs (MUSs) which talk to localhost only as well as
		fetchmail. External connections are impossible when
	        127.0.0.1 is entered here, as this will disable listening
		on public network interfaces.
	      </para>
	      <para>
	        Do not change this unless you know what you are doing.
		Altering this value could post a security risk to your
		system. For most users, the default value is sufficient.
	      </para>
          </section>
	  <section> <title>Other destinations for which mail is accepted</title>
	      <para>
	         Please enter a semicolon-separated list of recipient
		 domains for which this machine should consider itself
		 the final destination. These domains are commonly
                 called 'local domains'. The local hostname and 'localhost'
		 are always added to the list given here.
	      </para>
	      <para>
                 By  default  all  local    domains  will   be  treated
		 identically.  If   both a.example and  b.example   are
		 local  domains, acc@a.example   and acc@b.example will
		 be delivered to the  same final   destination.      If
		 different  domain names should be treated differently,
		 it is necessary to edit the config files afterwards.
	      </para>
              <para>
	        The answer to this question ends up in the list of
		domains that Exim will consider local domains. Mail
		for recipients in one of these domains will be
		subject to local alias expansion and then delivered
		locally in the appropriate configuration types.
	      </para>
          </section>
	  <section> <title>Domains to relay mail for</title>
	      <para>
	        Please enter a semicolon-separated list of recipient
		domains for which this system will relay mail, for
		example as a fallback MX or mail gateway. This means
		that this system will accept mail for these domains
	        from anywhere on the Internet and deliver them
	        according to local delivery rules.
	      </para>
	      <para>
                Do not mention local domains here. Wildcards may be used.
	      </para>
              <para>
                The answer to this question is a list of the domains
		for which Exim will relay messages coming in from anywhere
		on the Internet.
	      </para>
          </section>
	  <section> <title>Machines to relay mail for</title>
	      <para>
	         Please enter a semicolon-separated list of IP address
		 ranges for which this system will unconditionally relay
		 mail, functioning as a smarthost.
	      </para>
	      <para>
                 You should use the standard address/prefix format
		 (e.g. 194.222.242.0/24 or 5f03:1200:836f::/48).
	      </para>
	      <para>
                 If this system should not be a smarthost for any
		 other host, leave this list blank.
	      </para>
	      <para>
	        Please note that systems not listed here can still use
		SMTP AUTH to relay through this system. If this system
		only has clients on dynamic IP addresses that use SMTP
		AUTH, leave this list blank as well. Do
		<emphasis>NOT</emphasis> list 0.0.0.0/0!
	      </para>
	      <para>
		Warning: While it is possible to use 
		host<emphasis>names</emphasis> instead of IP addresses in this
		list extra care needs to be taken in this case. 
		<emphasis>Unresolvable names in the host list will break
		relaying.</emphasis> See
		Exim specification chapter <phrase>"Domain, host, address, and
		local part lists"</phrase>
		and the exim4-config_files man page.
	      </para>
          </section>
	  <section> <title>IP address or host name of the outgoing
              smarthost</title>
	      <para>
	        Please enter the IP address or the host name of a mail
		server that this system should use as outgoing
		smarthost. If the smarthost only accepts your mail on
		a port different from TCP/25, append two colons and
		the port number (for example smarthost.example::587 or
		192.168.254.254::2525). Colons in IPv6 addresses need
		to be doubled.
	      </para>
	      <para>
	        If the smarthost requires authentication, please refer
		to <xref linkend="smtp-auth"/> for notes about setting
		up SMTP authentication.
	      </para>
	      <para>
	        Multiple smarthost entries are permitted, semicolon
		separated. Each of the hosts is tried, in the order
		specified (See Exim specification, chapter
		<phrase>"The manualroute router"</phrase>, section
		<phrase>"How the list of hosts is used"</phrase>.)
	      </para>
          </section>
	  <section> <title>Hide local mail name in outgoing mail</title>
              <para>
	        The headers of outgoing mail can be rewritten to make
		it appear to have been generated on a different
		system, replacing the local host name in From,
		Reply-To, Sender and Return-Path.
              </para>
          </section>
	  <section> <title>Visible domain name for local users</title>
              <para>
	        If you ask Exim to hide the local mail name in
		outgoing mail, it will next ask you for the domain
		name that should be visible for your local users.
		These information is then used to establish the
		appropriate rewriting rules.
              </para>
          </section>
	  <section> <title>Keep number of DNS queries minimal
              (Dial-on-Demand)</title>
	      <para>
	         In normal mode of operation Exim does DNS lookups at
		 startup, and when receiving or delivering messages.
		 This is for logging purposes and allows keeping down
		 the number of hard-coded values in the configuration.
	      </para>
	      <para>
                 If this system does not have a DNS full service
		 resolver available at all times (for example if its
		 Internet access is a dial-up line using
		 dial-on-demand), this might have unwanted
		 consequences. For example, starting up Exim or
		 running the queue (even with no messages waiting)
		 might trigger a costly dial-up-event.
	      </para>
	      <para>
                 This option should be selected if this system is
		 using Dial-on-Demand. If it has always-on Internet
		 access, this option should be disabled.
	      </para>
          </section>
	  <section><title>Delivery method for local mail</title>
	      <para>
	        Exim is able to store locally delivered mail in
		different formats. The most commonly used ones are
		mbox and Maildir. mbox uses a single file for the
		complete mail folder stored in /var/mail/. With
		Maildir format every single message is stored in a
		separate file in ~/Maildir/.
	      </para>
	      <para>
	        Please note that most mail tools in Debian expect the
		local delivery method to be mbox in their default.
	      </para>
	  </section>
	  <section> <title>Split configuration into small files</title>
              <para>
	        Our packages offer two (actually three, see
		<xref linkend="completely-different-configuration"/>)
		possibilities:
              </para>	
              <orderedlist>
    	          <listitem>	
    	              <simpara>
		          Generate Exim's configuration from
			  <filename>/etc/exim4/exim4.conf.template,</filename>
			  which is basically a normal Exim run-time
			  configuration file which will be supplemented
			  with some macros generated from Debconf in a
			  post-processing step before it is passed to exim.
		      </simpara>
		  </listitem>
		  <listitem>
		      <simpara>
			  Generate Exim's configuration from the
			  multiple files in
			  <filename>/etc/exim4/conf.d/</filename>. The
			  directories in
			  <filename>/etc/exim4/conf.d/</filename>
			  correspond to the sections of the Exim
			  run-time configuration file, so you should
			  easily find your way around there.
		      </simpara>
		  </listitem>
	      </orderedlist>
              <para>
	        Splitting the configuration across multiple files
		means that you have the actual configuration file
		automatically generated from the files below
		<filename>/etc/exim4/conf.d/</filename> by invoking
		<command>update-exim4.conf</command>. Each section
		of Exim's configuration has its own subdirectory and
		the files in there are supposed to be read in
		alphanumeric order.
		<filename>router/00_exim4-config_header</filename>
		is followed by
		<filename>router/100_exim4-config_domain_literal</filename>,
		...
              </para>
              <para>
    	        If you chose unsplit configuration,
		<command>update-exim4.conf</command> builds the
		configuration from
		<filename>/etc/exim4/exim4.conf.template</filename>,
		which is basically the files from
		<filename>/etc/exim4/conf.d/</filename> concatenated
		together at package build time, and thus guarantees
		consistency on the target system.
              </para>
              <para>
    	        In both cases, <command>update-exim4.conf</command>
		generates exim configuration macros from the debconf
		configuration values and puts them into
		the actual configuration file, which is then used by
		the Exim daemon. See the
		<command>update-exim4.conf</command> manual
		page for more in-depth information about this
		mechanism.
              </para>
              <para>
    	        Benefits of the split configuration approach:
    		<itemizedlist>
    	  	    <listitem>
    	    	        <simpara>
                          it means less work for you when upgrading.
			  If we shipped one big file and modified
			  for example the Maildir transport in a new
			  version you won't have to do manual
			  conffile merging unless you had changed
			  exactly <emphasis>this</emphasis>
			  transport.
			</simpara>
		    </listitem>
		    <listitem>
		        <simpara>
			  It allows other packages (e.g. sa-exim) to
			  modify Exim's configuration by dropping
			  files into
			  <filename>/etc/exim4/conf.d</filename>.
			  This needs, however quite exact syncing
			  between the exim4 packages and the other,
			  cooperating package.
			</simpara>
		    </listitem>
		</itemizedlist>
	      </para>
	      <para>
		Drawbacks of the split configuration approach:
		<itemizedlist>
		    <listitem>
		        <simpara>
			  It is more fragile. If files from
			  different sources (package, manually
			  changed, or other package) get out of
			  sync, it is possible for Exim to break
			  until you manually correct this. This can
			  for example happen if we decide to add a
			  new option to the Debian setup of a later
			  version, and you have already set this
			  option in a local file.
			</simpara>
		    </listitem>
		</itemizedlist>
	      </para>
	      <para>
	        Benefits of the unsplit configuration approach:
		<itemizedlist>
		    <listitem>
		        <simpara>
			  People familiar with configuring Exim may
			  find this approach easier to understand as
			  <filename>exim4.conf.template</filename>
			  basically is a complete Exim configuration
			  file which will only undergo some basic
			  string replacement before is it passed to
			  exim.
		        </simpara>
		    </listitem>
		    <listitem>
			<simpara>
			  Split-config's fragility mentioned
			  above does not occur.
			</simpara>
		    </listitem>
		</itemizedlist>
	      </para>
	      <para>
	        Drawbacks of the unsplit configuration approach:
		<itemizedlist>
		    <listitem>
		        <simpara>
			  Will require manual intervention in case of an
			  upgrade.
			</simpara>
		    </listitem>
		</itemizedlist>
	      </para>
              <para>
                If in doubt go for the unsplit config, because it is
		easier to roll back to Debian's default configuration
		in one step. If you intend to do many changes to the
		Debian setup, you might want to use the split config
		at the price of having to more closely examine the
		config file after an update.
	      </para>
	      <para>
	        We'd appreciate a patch that uses ucf and the
		3-way-merge mechanism offered by that package. It
		might be the best way to handle the big configuration
		file.
	      </para>
	      <para>
	        If you are using unsplit configuration, have local
		changes to <filename>/etc/exim4/conf.d/</filename>
		(either made by yourself or by other packages dropping
		their own routers or transports in) and want to
		re-generate
		<filename>/etc/exim4/exim4.conf.template</filename> to
		activate these changes, you can do so by using
		<command>update-exim4.conf.template</command>.
	      </para>
	  </section>
      </section>
      <section> <title>Access Control in the default configuration</title>
        <para>
          The Debian exim 4 packages come with a default configuration
	  that allows flexible access control and blacklisting of
	  sites and hosts. The acls involved can be found in
	  /etc/exim4/conf.d/acl, or in /etc/exim4/exim4.conf.template,
	  depending on which configuration scheme you use. Most
	  rejections of messages due to this mechanism happen at RCPT
	  time. Local configuration of the mechanisms happens through
	  data files in /etc/exim4 or via Exim macros that you can set
	  in /etc/exim4/conf.d/main, so there is normally no need to
	  change the files in the acl subdirectory in a split-config
	  setup. If you use the non-split config, you need to edit
	  /etc/exim4/exim4.conf.template, which, as a big
	  dpkg-conffile, won't give you any advantage of the .ifdef
	  scheme.
        </para>
        <para>
          The data files are documented in the exim4-config_files man
          page.
        </para>
        <para>
          The access lists delivered with the exim4 packages also
	  contain quite a few configuration options that are too
	  restrictive to be active by default on a real-life site.
	  These are masked by .ifdef statements, can be activated by
	  setting the appropriate macros, and are documented in the
	  ACL files itself.
        </para>
    </section>
    <section id='macros'> <title>Using Exim Macros to control the
      configuration</title>
      <para>
	Our configuration can be controlled in a limited way by
	setting macros. That way, you can switch on and off certain
	parts of the default configuration and/or override values set
        in Debconf without having to touch the dpkg-conffiles. While
	touching dpkg-conffiles itself is explicitly allowed and wanted,
	it can be quite a nuisance to be asked on package upgrade
	whether one wants to use the locally changed file or the
	file changed by the package maintainer.
      </para>
      <para>
	Whenever you see an <command>.ifdef</command> or
	<command>.ifndef</command> clause in the configuration file,
	you can control the appropriate clause by setting the macro in
	a local configuration file. <command>.ifndef</command> checks
	whether a specific macro is set (to a nonempty value), the
	actual value does not matter. (Both
	<quote>EXIM4_EXAMPLE = true</quote> and
	<quote>EXIM4_EXAMPLE = false</quote> pass this test.)
	For split configuration, you can
	drop the local configuration file anywhere in
	<filename>/etc/exim4/conf.d/main</filename>. Just make sure it
	gets read before the macro is first used. 
	<filename>000_localmacros</filename> is a possible name,
	guaranteeing first order. For a non-split configuration,
	<filename>/etc/exim4/exim4.conf.localmacros</filename> gets
	read before
	<filename>/etc/exim4/exim4.conf.template</filename>. To
	actually set the macro <varname>EXIM4_EXAMPLE</varname> to the
	value "this is a sample", write the following line
      </para>
      <para>
	EXIM4_EXAMPLE = this is a sample
      </para>
      <para>
	into the appropriate file. For more detailed discussion of the
	general macro mechanism, see the Exim specification, chapter
	<phrase>"The Exim run time configuration file"</phrase>, for
	details how macro expansion works.
      </para>
      </section>
      <section>	<title>How does this work?</title>
	<para>
	  The script <command>update-exim4.conf</command> parses the
	  <filename>/etc/exim4/update-exim4.conf.conf</filename> file
	  and provides the configuration for the exim daemon.
	</para>
	<para>
	  Depending on the value of
	  <varname>dc_use_split_config</varname>, it either
	  <itemizedlist>
	    <listitem>
	      <simpara>
		takes all the files below
		<filename>/etc/exim4/conf.d/</filename> and
		concatenates them together or
	      </simpara>
	    </listitem>
	    <listitem>
	      <simpara>
		uses <filename>exim4.conf.template</filename> as
		input.
	      </simpara>
	    </listitem>
	  </itemizedlist>
	  The debconf-managed information from
	  <filename>/etc/exim4/update-exim4.conf.conf</filename> is
	  merged into the generated configuration file by generating a
          number of Exim configuration macros.
	</para>
	<para>
	  <varname>DCsmarthost</varname>, for example, is set to the
	  value of <varname>$dc_smarthost</varname>
	  in <filename>/etc/exim4/update-exim4.conf.conf</filename>
	  which holds the answer to "Which machine will act as the
	  smarthost and handle outgoing mail?"
	</para>
	<para>
	  The result of these operations is saved as
	  <filename>/var/lib/exim4/config.autogenerated</filename>,
	  which is <emphasis>not</emphasis> a dpkg-conffile! Manual
	  changes to this file will be overwritten by
	  <command>update-exim4.conf</command>.
	</para>
	<para>
	  Please consult <command>update-exim4.conf</command> manpage
	  for more detailed information.
	</para>
	<para>
	  <command>update-exim4.conf</command> is invoked by the init
	  script prior to any operation that may invoke an exim process,
	  and gives an error message if the generated config file is
	  syntactically invalid. If you want to activate your changes to
	  files in conf.d/ just execute <command>invoke-rc.d exim4 restart</command>.
	</para>
      </section>
      <section id="howto-change-config"><title>How do I do minor tweaks to the configuration?</title>
        <para>
	  Some times, you want to do minor adjustments to the Exim
	  configuration to make Exim behave exactly like you want it
	  to behave. There are the following possibilities to modify
	  Exim's behavior.
	</para>
	<section><title>Adjustments supported by the debconf configuration</title>
	  <para>
	    If you want to modify parameters that are supported by the
	    debconf configuration, things are easy. Just invoke
	    <command>dpkg-reconfigure exim4-config</command> or hand-edit
	    <filename>/etc/exim4/update-exim4.conf.conf</filename> to your
	    liking and restart Exim.
	  </para>
	  <para>
	    You can find explanation of the debconf questions in <xref
            linkend="debconf-questions"/>.
            Additionally,
	    <filename>/etc/exim4/update-exim4.conf.conf</filename>
	    is documented in the <command>update-exim4.conf</command>
	    man page.
	  </para>
	</section>
	<section><title>Adjustments controlled by macros in the Debian Exim configuration</title>
	  <para>
	    Some aspects of the Debian Exim configuration can be
	    controlled by Exim macros. To find out about these, you
	    need basic understanding of Exim configuration. Just look
	    in our Exim configuration and see which macro needs to be
	    set to a different value to alter Exim's behavior.
	  </para>
	  <para>
	    <xref linkend="macros"/> gives a closer explanation about
            how to do this.
	  </para>
	</section>
	<section><title>Making direct changes to the Debian Exim configuration</title>
	  <para>
	    You can, of course, make direct change to the
	    configuration. All configuration files in /etc/exim4 are
	    dpkg-conffiles, and you can thus edit them any time. Your
	    changes will be preserved through updates. You need to
            know about how to configure Exim to be successful.
	  </para>
	  <para>
	    If you use unsplit configuration, edit
            <filename>/etc/exim4/exim4.conf.template</filename>. If you use
	    split configuration, edit the Exim configuration snippets in
	    <filename>/etc/exim4/conf.d</filename>.
	  </para>
	  <para>
	    More information about how the Exim configuration is built
            can be found in this document and in the
	    <command>update-exim4.conf</command> manual page.
	  </para>
	</section>
      </section>
      <section id="completely-different-configuration">	<title>Using a completely different configuration scheme</title>
	<para>
	  If you are an experienced Exim administrator, you might feel
	  working with our pre-fabricated configuration
	  cumbersome and complex. You might feel right if you need to
	  make more complex changes and do not need to receive updates
	  from us. This section is going to tell about how to use
	  your own configuration.
	</para>
	<para>
	  But, you might profit from keeping the Debian magic. Most
	  files that come with Debian exim4 are conffiles. Debian is
	  going to care about your changes and keeps them around.
	  Additionally, a lot of configuration options can be
	  overridden with a macro, which does not require you to
	  actually change our configuration file. A lot of people are
	  using our configuration scheme, and maybe it is going to
	  save you a lot of time if you decide to spend some time
	  familiarizing yourself with our scheme.
	</para>
	<section> <title>Override exim4-config configuration magic</title>
	    <para>
	    	If you are only running a small number of systems and
		want to completely disable Debian's magic, just take
		your monolithic configuration file and install it as
		<filename>/etc/exim4/exim4.conf</filename>. Exim will
		use that file verbatim. To have something to start,
		you can either take
		<filename>/etc/exim4/exim4.conf.template</filename>, 
		run <command>update-exim4.conf --keepcomments --output
		/etc/exim4/exim4.conf</command>, or use upstream's
		default configuration file that is installed as
		<filename>/usr/share/doc/exim4-base/examples/example.conf.gz</filename>.
		You are going to lose all magic you get from packaging
		though, so you need to be familiar with Exim to build
		an actually working config.
	    </para>
	    <para>
		<filename>/var/lib/exim4/config.autogenerated</filename>,
		the file generated by
		<command>update-exim4.conf</command>, is ignored as soon
		as <filename>/etc/exim4/exim4.conf</filename> is found. 
		You should not edit
		<filename>/etc/exim4/exim4.conf</filename> directly when
		Exim is running, because the forked processes Exim starts
		for SMTP receiving or queue running would use the new
		configuration file, while the original main exim-daemon
		would still use the old configuration file.
	    </para>
	    <para>
	    	Some third-party HOWTOs that reference Debian and
		claim to make things easy suggest dumping a
		pre-fabricated, static config file to
		<filename>/etc/exim4/exim4.conf</filename>. This is
		considered bad advice by the Debian maintainers since
		you are going to disable all updates and service magic
		that Debian might deliver in the future this way. If
		you do not know exactly what you're doing here, this
		is a bad choice. We try to comment on external HOWTOs
		found on the web in the <ulink
		url="http://wiki.debian.org/PkgExim4UserFAQ">Debian
		Exim4 User FAQ</ulink> to help you find out which
		advice to follow.
	    </para>
	</section>
	<section> <title>Replacing exim4-config with your own exim4 configuration package.</title>
	    <para>
		We split off Exim's configuration system (debconf,
		<command>update-exim4.conf</command>, and the files in
		<filename>/etc/exim4/conf.d)</filename> to a separate
		package, exim4-config. If you want to, you can replace
		exim4-config by something entirely different. The other
		packages don't care. Your package needs to:
		<itemizedlist>
		  <listitem>
		    <simpara>
			Provides: exim4-config-2, Conflicts:
			exim4-config-2,exim4-config
		    </simpara>
		  </listitem>
		  <listitem>
		    <simpara>
			drop the Exim 4 configuration either into
			<filename>/var/lib/exim4/config.autogenerated</filename>
			or into <filename>/etc/exim4/exim4.conf</filename>.
		    </simpara>
		  </listitem>
		</itemizedlist>
		Your package must provide an executable <command>update-exim4.conf</command>
		that must be in root's path (<filename>/usr/sbin</filename> recommended). The init
		script will invoke that executable prior to invoking the
		actual exim daemon. If you do not need that script, have it exit 0.
	    </para>
	    <para>
		If you want to create your own configuration packages, there is a
		number of helpers available.
		<itemizedlist>
	 	  <listitem>
		    <simpara>
			The Exim 4 Debian svn repository holds sources for a
			exim4-config-simple package which contains a simple, not
			debconf-driven configuration scheme as an example which can
			be used as a template for a classical, exim4.conf based
			configuration scheme.
		    </simpara>
		  </listitem>
		  <listitem>
		    <simpara>
			The Exim 4 Debian svn repository holds sources for a
			exim4-config-medium package which contains the conf.d
			driven configuration of the main package with the
			debconf interaction removed. This can be used to create
			your own non-debconf configuration package that uses the
			conf.d mechanism.
		    </simpara>
		  </listitem>
		  <listitem>
		    <simpara>
			Finally, you can invoke the script
			<filename>debian/config-custom/create-custom-config-package</filename>
			which will create a new source package
			"exim4-config-custom" with the debconf-driven config
			scheme of exim4-config for your local modification.
		    </simpara>
		  </listitem>
		</itemizedlist>
		Please note that exim4-config-simple and
		exim4-config-medium are only targeted to be used as a
		template. The configurations contained are not
		suitable for productive use. Of course, the Debian
		maintainers appreciate any patches you might find
		suitable. The scripts in exim4-config-simple and
		exim4-config-medium may not work at all in your
		environment. Unfortunately, they have not been
		updated in a long time as well. We are willing to
		accept patches.
	    </para>
	    <para>
		See the development web page for links to the subversion
		repository.
	    </para>
	    <para>
		Exchanging the entire exim4-config package with
		something custom comes particularly handy for sites
		that have more than a few machines that are
		similarly configured, but do not want to use the
		original exim4-config package. Build your own
		exim4-config-custom or exim4-config-foo, and simply
		 apt that package to the machines that need to have
		that configuration.  Future updates can then be
		handled via the dpkg-conffile mechanism, properly
		detecting local modifications.
	    </para>
	    <para>
		In the future, it might be possible that Debian will
		contain multiple flavours of Exim4 configuration.
		However, these packages would have to be maintained
		by someone else because the exim4 package
		maintainers think that the scheme delivered with
		exim4-config is the least of all evils and would
		rather not spend the time to maintain multiple configuration
		schemes while only actually using one. It would be
		nice to have a configuration scheme using a
		monolithic config file, managed by ucf in
		three-way-merge mode. If anybody feels ready to
		maintain it, please go ahead.
	    </para>
	</section>
      </section>
    </section>
    <section id="TLS"> <title>Using TLS</title>
    <para>
      Both exim4-daemon-heavy and exim4-daemon-light support TLS/SSL
      using the GnuTLS library.
    </para>
      <section>	<title>Exim 4 as TLS/SSL client</title>
	<para>
	  Exim will use TLS
	  via STARTTLS <emphasis>automatically</emphasis> as client if
	  the server Exim connects to offers it.
	</para>
	<para>
	  This means that you will not need any special configuration if
	  you want to use opportunistic TLS for outgoing mail. However,
	  to enforce TLS and successful certificate verification, a few
	  things need to be configured.
	</para>
	<para>
		To enforce TLS and prevent fallback to unencrypted
		connections, ensure that hosts_require_tls = * is in effect on
		the respective transport.  For the remote_smtp_smarthost
		transport, this setting can be controlled via the
		REMOTE_SMTP_SMARTHOST_HOSTS_REQUIRE_TLS macro.
	</para>
	<para>
		The certificate presented by the remote host is checked
		against the system CA certificate store
		(<filename>/etc/ssl/certs/</filename>) and the verification
		result is logged (CV=...).
		For the remote_smtp_smarthost transport successful
		certificate verification against the system trust store is
		enforced by default on encrypted connections.
		(<quote>REMOTE_SMTP_SMARTHOST_TLS_VERIFY_HOSTS = *</quote>
		is set by default). Set this macro to an empty value to
		disable this. To check against a certificate not present in
		the system trust store point
		REMOTE_SMTP_SMARTHOST_TLS_VERIFY_CERTIFICATES (which sets
		tls_verify_certificates) to a file containing this (set of)
		trusted certificates.
	</para>
	<para>
                Successful certificate verification is
                <emphasis>not enforced</emphasis>
		by default for other transports.
	</para>
	<para>
		Another possibility would be to use DANE for certificate
		verification. This requires support on the server side and
		a resolver with DNSSEC support on the client side.
	</para>
	<para>
	  If your
	  server setup mandates the use of client certificates, you
	  need to amend your remote_smtp and/or remote_smtp_smarthost
	  transports with a tls_certificate option. This is not
          commonly needed.
	</para>
	<para id="tls_client_certicate">
		To make exim send a TLS certificate to the remote host set
		REMOTE_SMTP_TLS_CERTIFICATE/REMOTE_SMTP_PRIVATEKEY or for
		the remote_smtp_smarthost transport
		REMOTE_SMTP_SMARTHOST_TLS_CERTIFICATE/REMOTE_SMTP_SMARTHOST_PRIVATEKEY
		respectively.
	</para>
	<para>
		To use TLS on connect set <quote>protocol = smtps</quote> on
		the respective transport. (For the remote_smtp_smarthost
		transport the macro REMOTE_SMTP_SMARTHOST_PROTOCOL can be used.
	</para>
      </section>
      <section>	<title>TLS support for Exim as server</title>
	<para>
                Incoming TLS is enabled by default. It can be disabled by
                setting MAIN_TLS_ADVERTISE_HOSTS to an empty value.
	</para>
	<para>
                The MAIN_TLS_ENABLE macro allows setting/finetuning exim's
                TLS options. If it is not set upstream defaults will be
                used. Exim will then use on-connect autogenerated self-signed
                certificates. This is not optimal both for performance
                reasons and because these certificates cannot be verified by
                connecting clients/servers.
	</para>
  <para>
    Each time an on-demand cert is created exim will log a info message
    in the mainlog that looks like this:
      <blockquote>
        Warning: No server certificate defined; will use a selfsigned one.
        Suggested action: either install a certificate or change
        tls_advertise_hosts option
      </blockquote>
    This informative message can be ignored.
  </para>
  <para>
    To avoid the (small) performance issue and the log message one can
    locally create certificates. The exim-gencert script (which requires
    openssl) can be helpful for this purpose. It is shipped in
	  <filename>/usr/share/doc/exim4-base/examples/</filename> and
	  takes care of proper access privileges on the private key
	  file when installing key/certificate in
	  <filename>/etc/exim4/</filename>.
	</para>
	<para>
    One can also get a certificate from a CA and install the key in
    <filename>/etc/exim4/exim.key</filename> and the certificate
    in <filename>/etc/exim4/exim.crt</filename>.
	</para>
	<para>
	  To enable use of the installed certificates set the macro
    MAIN_TLS_ENABLE in a local configuration file as described in
    <xref linkend="macros"/>.
	</para>
	<para>
	  Exim will advertise STARTTLS when
	  connected to on the normal SMTP ports. Alternatively/additionally
	  TLS on connect on Port 465 can be enabled by including
	  <code>-oX 465:25 -oP /run/exim4/exim.pid</code>
	  in EXIMSERVICE/EXIMDAEMONOPTS in
	  <filename>/etc/default/exim4</filename> and
	  "tls_on_connect_ports=465" in the main configuration section.
	</para>
	<para>
	  The -oP is needed because Exim does not write an implicit pid
	  file if -oX is given. Without pid file, service file/init-script
	  and cronjob will malfunction.
	</para>
	<para>
	  It might be appropriate to add "+tls_cipher" to
	  any log_selector statement you might already have, or to add a
	  log_selector statement setting these two options in a local
	  configuration file. (For Debian's configuration simply define
	  the MAIN_LOG_SELECTOR macro.)
	  This option makes Exim log what cipher
	  your Exim and the peer's mailer have negotiated to use to
	  encrypt the transaction.
	</para>
	<para>
	  Exim can be configured to ask a client for a certificate and to
	  try to verify it. Debian's exim configuration used to enable
	  this by default, but stopped doing so since it caused TLS errors
	  with a couple of popular clients (Outlook, Incredimail, etc.).
	  To enable this again set the macro MAIN_TLS_TRY_VERIFY_HOSTS to
	  the lists hosts whose certificates you want to check. (Use * to
	  try checking all hosts. The value of the macro is used to
	  populate exim's main option tls_try_verify_hosts.) You should
	  also point MAIN_TLS_VERIFY_CERTIFICATES to a file containing the
	  accepted certificates, since its default setting
	  (/etc/ssl/certs/ca-certificates.crt) can contain a large list of
	  certificates which causes the interoperabilty problems with
	  Outlook et.al. noted above.
	</para>
	<para>
		The server certificate is only used for incoming connections,
		please consult <xref linkend="tls_client_certicate"/> for the
		corresponding outgoing conncection options.
	</para>
      </section>
      <section>	<title>Troubleshooting</title>
	<para>
	  If Exim complains in an SMTP session that TLS is unavailable,
	  the Exim mainlog or paniclog frequently has exact information
	  about what might be wrong. Fo example, you might see
	</para>
	<para>
	  2003-01-27 19:06:45 TLS error on connection from localhost [127.0.0.1]
	  (cert/key setup): Error while reading file)
	</para>
	<para>
	  showing that there has been an error while accessing the
	  certificate or the private key file.
	</para>
	<para>
	  Insuffient entropy available is a frequent cause of TLS
          failures in Exim context. If Exim logs "not enough random bytes
	  available", or simply hangs silently when an encrypted
          connection should be established, then Exim was
	  unable to read enough random data from
	  <filename>/dev/random</filename> to do whatever cryptographic
	  operation is requested. Please check that your
	  <filename>/dev/random</filename> device is setup properly.
	</para>
	<para>
	  You might also find "TLS error on connection to [...]
	  (gnutls_handshake): The Diffie-Hellman prime sent by the server is
	  not acceptable (not long enough)." given as reason. Exim by default
	  requires a DH prime length of 1024 bits. This requirement can be
	  downgraded by setting the tls_dh_min_bits option on the SMTP
	  transport.  The setting is accessible in the Debian configuration by
	  setting the macro TLS_DH_MIN_BITS. (e.g. "TLS_DH_MIN_BITS = 768").
	</para>
      </section>
    </section>
    <section id="smtp-auth"> <title>SMTP-AUTH</title>
      <para>
        Exim can do SMTP AUTH both as a client and as a server.
      </para>
      <para>
	AUTH PLAIN and AUTH LOGIN are disabled for connections which are
	not protected by SSL/TLS per default. These authentication
	methods use cleartext passwords, and allowing the
	transmission of cleartext passwords on unencrypted connections
	is a security risk. Therefore, the default configuration configures
	Exim not to use and/or allow AUTH PLAIN and AUTH LOGIN over
        unencrypted connections.
      </para>
      <para>
        It is thus recommended to set up Exim to use TLS to encrypt
        the connections. Please refer to <xref linkend="TLS"/> for
        documentation about this. Note that most Microsoft clients
        need special handling for TLS.
      </para>
      <section>	<title>Using Exim as SMTP-AUTH client</title>
	<para>
	  If you want to set up Exim as SMTP AUTH client for delivery
	  to your internet access provider's smarthost put the name of
	  the server, your login and password in
	  <filename>/etc/exim4/passwd.client</filename>. See the man
          page for exim4-config_files(5) for more information about the
	  required format.
	</para>
	<para>
	  If you need to enable AUTH PLAIN or AUTH LOGIN for unencrypted
	  connections because your service provider does support neither
	  TLS encryption nor the CRAM MD5 authentication method, you can
	  do so by setting the AUTH_CLIENT_ALLOW_NOTLS_PASSWORDS macro.
	  Please refer to <xref linkend="macros"/> for an explanation of
	  how best to do this.
	</para>
	<para>
	  <filename>/etc/exim4/passwd.client</filename> needs to be
	  readable for the exim user (user Debian-exim, group
	  Debian-exim). It is suggested that you keep the default
	  permissions root:Debian-exim 0640.
	</para>
      </section>
      <section>	<title>Using Exim as SMTP-AUTH server</title>
	<para>
	  The configuration files include many, verbosely commented,
	  examples for server-side smtp-authentication which just need
	  to be uncommented.
	</para>
	<para>
	  If you need to enable AUTH PLAIN or AUTH LOGIN for unencrypted
	  connections because your clients neither support TLS encryption
	  nor the CRAM MD5 authentication method, you can do so by setting
	  the AUTH_SERVER_ALLOW_NOTLS_PASSWORDS macro. Please refer to
	  <xref linkend="macros"/> for an explanation of how best to
	  do this.
	</para>
	<para>
	  If you want to authenticate against system passwords (e.g. 
	  <filename>/etc/shadow</filename>) the easiest way is to use
	  saslauthd in the Debian package sasl2-bin. You have to add the
	  exim-user (currently Debian-exim) to the sasl group, to give
	  exim permission to use the saslauthd service.
	</para>
	<para>
	  The Debian exim4 maintainers consider using system login
	  passwords a bad idea for the following reasons:
	  <itemizedlist>
	    <listitem>
	      <simpara>
	        A compromised password will give access to a system account.
	      </simpara>
	    </listitem>
	    <listitem>
	      <simpara>
	        E-Mail passwords could accidentally be transmitted unencrypted.
	      </simpara>
	    </listitem>
	    <listitem>
	      <simpara>
	        E-Mail passwords are likely to be stored with the
                client software, which greatly increases the chance of a
		compromise.
	      </simpara>
	    </listitem>
	  </itemizedlist>
	</para>
      </section>
    </section>

    <section> <title>How the Exim daemon is started</title>
      <para>
        The Debian Exim 4 packages' init script is located in
	<filename>/etc/init.d/exim4</filename>. Apart from the
	functions that are required by Debian policy and the LSB, it
	supports the commands <command>what</command>, which executes
	<command>exiwhat</command> to show what your Exim processes
	are doing, and <command>force_stop</command> which
	unconditionally kills all Exim processes.
      </para>
      <para>
        The init script can be configured to start listening and/or
	queue running daemons. This configuration can be found in
	<filename>/etc/default/exim4</filename>. This file is
	extensively documented.
      </para>
    </section>

    <section> <title>Miscellaneous packaging issues</title>
      <section> <title>The daily cron job</title>
	  <para>
	    Exim4's daily cron job
            (<filename>/etc/cron.daily/exim4-base</filename>)
	    does basic housekeeping tasks:
	    <itemizedlist>
	      <listitem>
	        <simpara>
		  It reads <filename>/etc/default/exim4</filename>, so you
		  can use this file to change any of the variables used in
		  the cron job.
	        </simpara>
	      </listitem>
	      <listitem>
	        <simpara>
		  It is a no-op if no Exim4 binary is found.
	        </simpara>
	      </listitem>
	      <listitem>
	        <simpara>
		  If <command>$E4BCD_DAILY_REPORT_TO</command> is set
		  to a non-empty string, the output of eximstats is
		  mailed to the address given in that variable. The
                  default is empty, so no reports are sent. Options
                  for eximstats can be given in
                  <command>$E4BCD_DAILY_REPORT_OPTIONS</command>.
	        </simpara>
	      </listitem>
	      <listitem>
	        <simpara>
		  A non-empty paniclog is a nearly sure sign of bad
		  things going on. Thus, the cron job will send out
		  warning messages to the syslog and root if it finds
		  the panic log non-empty.
		  Please note that the paniclog is not rotated daily,
		  so existing issues will be reported daily until
		  either the paniclog is rotated due to its sheer
		  size, or you manually move it away, for example by
		  calling <command>logrotate -f
		  /etc/logrotate.d/exim4-paniclog</command> from a shell.
	        </simpara>
		<simpara>
		  Just in case your system logs transient error
		  situations to the panic log as well (see, for
		  example,
		  <ulink url="https://bugs.exim.org/show_bug.cgi?id=92">Exim Bug 92</ulink>),
		  you can configure
		  <command>$E4BCD_PANICLOG_NOISE</command> to a
		  regular expression. If the paniclog contains only
		  lines that match that regular expression, no warning
		  messages are generated.
	        </simpara>
		<simpara>
		  If you want to disable paniclog monitoring
		  completely, set <command>$E4BCD_WATCH_PANICLOG</command>
		  to no. <command>E4BCD_WATCH_PANICLOG=once</command> will
		  rotate a non-empty paniclog automatically after sending out
		  the warning e-mail.
	        </simpara>
		<simpara>
		  The <command>E4BCD_PANICLOG_LINES</command> setting can be
		  used to limit the number of lines of paniclog quoted in
		  warning email. It is set to 10 by default.
		</simpara>
	      </listitem>
	      <listitem>
	        <simpara>
		  It tidies up the retry and hints databases.
	        </simpara>
	      </listitem>
	    </itemizedlist>
	  </para>
      </section>
    </section>

    <section> <title>Using Exim with inetd/xinetd</title>
      <para>
	Exim4 is run as a separate daemon instead of inetd/xinetd for
	two reasons:
	<variablelist>
	  <varlistentry>
	    <term>Ease of maintenance:</term>
	    <listitem>
	      <simpara>
		update-inetd is difficult to impossible to handle
		correctly (Just check the archived bug reports of Exim.) 
		and update-inetd seems to be unmaintained for a long
		time, nobody dares to touch it. To quote Mark Baker, the
		maintainer of Exim (v3): "I really wish I had never used
		inetd in the first place, but simply set up exim to run
		as a daemon, but it's too late to change that now."
	      </simpara>
	    </listitem>
	  </varlistentry>
	  <varlistentry>
	    <term>Extended features</term>
	    <listitem>
	      <simpara>
		Running from <command>inetd</command> interferes with
		Exim's resource controls (e.g it disables
		smtp_accept_max_per_host and smtp_accept_max).
	      </simpara>
	    </listitem>
	  </varlistentry>
	</variablelist>
      </para>
      <para>
	If you introduce bugs on your systems by running from (x)inetd
	you are on your own! If you want to run exim from
	<command>xinetd</command>, follow these steps:
	<orderedlist>
	  <listitem>
	    <simpara>
		Disable Exim 4's listening daemon by standard means
		for the local init system (e.g. mask the service
		with systemd) and take care of running the queue (e.g. with
		a cronjob).
	    </simpara>
	  </listitem>
	  <listitem>
	    <para>
	      Create <filename>/etc/xinetd.d/exim4</filename>
	      <programlisting>
service smtp
{
    disable     = no
    flags       = NAMEINARGS
    socket_type = stream
    protocol    = tcp
    wait        = no
    user        = Debian-exim
    group       = Debian-exim
    server      = /usr/sbin/exim4
    server_args = exim4 -bs
}
	      </programlisting>
	    </para>
	  </listitem>
	  <listitem>
	    <simpara>Run <command>invoke-rc.d exim4 restart; invoke-rc.d
(x)inetd restart</command></simpara>
	  </listitem>
	</orderedlist>
      </para>
      <para>If you want to use plain inetd,
	<orderedlist>
	  <listitem>
	    <simpara>
		Disable Exim 4's listening daemon by standard means
		for the local init system (e.g. mask the service
		with systemd) and take care of running the queue (e.g. with
		a cronjob).
	    </simpara>
	  </listitem>
	  <listitem>
	    <simpara>
         Insert following line into
         <filename>/etc/inetd.conf</filename>:<programlisting>
smtp stream   tcp     nowait  Debian-exim     /usr/sbin/exim4 exim4 -bs
         </programlisting>
      </simpara>
	  </listitem>
	</orderedlist>
      </para>
    </section>

    <section> <title>Handling incoming mail for local accounts with low UID</title>
      <para>
        Since system accounts (mail, uucp, lp etc) are usually aliased
	to root, and root's mailbox is usually read by a human, these
	account names have started to be a common target for spammers.
	The Debian Exim 4 packages have a mechanism to deal with this
	situation. However, since this derives rather far from normal
	behavior, it is disabled by default.
      </para>
      <para>
        To enable it, set the macro FIRST_USER_ACCOUNT_UID to a numeric,
	non-zero value. Incoming mail for local users that have a UID
	lower than FIRST_USER_ACCOUNT_UID is rejected with the message "no
	mail to system accounts". Incoming mail for local users that
	have a UID greater or equal FIRST_USER_ACCOUNT_UID are processed as
	usual. Therefore, the default value of 0 ensures that the
	mechanism is disabled. On Debian systems, setting
	FIRST_USER_ACCOUNT_UID to 500 or 1000 (depending on your local policy)
	will disable incoming mail for system accounts.
      </para>
      <para>
        Just in case that you need exceptions to the rule,
	<filename>/etc/exim4/lowuid-aliases</filename> is an alias
	file that is only honored for local accounts with UID lower
	than FIRST_USER_ACCOUNT_UID. If you define an alias for such an
	account here, incoming mail is processed according to the
	alias. If you alias the account to itself, messages are
	delivered to the account itself, which is an exception to the
	rule that messages for low-UID accounts are rejected. The
	format of <filename>/etc/exim4/lowuid-aliases</filename> is
	just another alias file.
      </para>
    </section>
    <section> <title>How to bypass local routing specialities</title>
      <para>
        Sometimes, it might be desirable to be able to bypass local
	routing specialities like the alias file or a user-forward
	file. This is possible in the Debian Exim4 packages by
	prefixing the account name with "real-". For a local account
	name "foo", "real-foo@hostname.example" will result in direct
	delivery to foo's local Mailbox.
      </para>
      <para>
        This feature is by default only available for locally
	generated messages. If you want it to be accessible for
	messages delivered from remote as well, set the Exim macro
	COND_LOCAL_SUBMITTER to true. If you do not want this at all,
	set the macro to false. Please note that the userforward
	router uses this feature to get error messages delivered, i.e.
	notifying the user of a syntax error in her
	<filename>.forward</filename> file.
      </para>
    </section>
    <section> <title>Using more complex deliveries from alias files</title>
      <para>
	Delivery to arbitrary files, directory or to pipes in the
	<filename>/etc/aliases</filename> file is disabled by default
	in the Debian Exim 4 packages. The delivery process including the
	program being piped to would run as the exim admin-user
	Debian-exim, which might open up security holes.
      </para>
      <para>
	Invoking pipes from <filename>/etc/aliases</filename> file is
	widely considered obsolete and deprecated. The Debian Exim
	package maintainers would like to suggest using a dedicated
	router/transport pair to invoke local processes for mail
	processing. For example, the Debian mailman package contains a
	<filename>/usr/share/doc/mailman/README.Exim4.Debian</filename> file
	that gives a good example how to implement this. Using a
	dedicated router/transport pair have the following advantages:
	<itemizedlist>
	  <listitem>
	    <para>
	      The router/transport pair can be put in place by another
	      package, giving a well-defined transaction point between
	      Exim 4 and $PACKAGE.
	    </para>
	  </listitem>
	  <listitem>
	    <para>
	      Not allowing pipe deliveries from alias files makes it
	      harder to accidentally run programs with wrong
	      privileges.
	    </para>
	  </listitem>
	  <listitem>
	    <para>
	      It is possible to run different pipe processes under
	      different accounts.
	    </para>
	  </listitem>
	  <listitem>
	    <para>
	      Even if only invoking a single local program, it is easier
	      to do with your dedicated router/transport since you won't
	      need to change this file, making automatic updates of this
	      file possible for future versions of the Exim 4 packages. If
	      you do local changes here, dpkg conffile handling will
	      bother you on future updates.
	    </para>
	  </listitem>
	</itemizedlist>
	If you insist on using <filename>/etc/aliases</filename> in
	the traditional way, you will need to activate the
	respective functions by setting the transport options on the
        system_aliases router appropriately. Macros are defined to make
	this easier. See
       
<filename>/etc/exim4/conf.d/router/400_exim4-config_system_aliases</filename>
	for information about which macros are available. You might
        find the address_file, address_pipe and/or address_directory
        transports that are used for the userforward router helpful in
	writing your own transports for use in the system_aliases router.
      </para>
      <para>
	If any of your aliases expand to pipes or files or directories
	you should set up a user and a group for these deliveries to run
	under. You can do this by setting the "user" and if a different
	one than the user's primary group is wanted also
	a "group" option.
	Alternatively, you can specify "user" and/or "group" on the
	transports that are used.
      </para>
    </section>

    <section> <title>Putting Exim 4 and UUCP together</title>
      <para>
	UUCP is a traditional way to execute remote jobs (e.g. spool
	mails), and as a lot of old things there are much more than one
	way to do it. However, today, the ways to handle it have boiled
	down to more or less two different ways.
      </para>
      <para>
	Our recommendation is to use bsmtp/rsmtp wherever possible,
	because it supports all kinds of mail addresses (also the empty
	ones in bounces), and is also better from the security point of
	view.
      </para>
      <section>	<title>Sending mail via UUCP</title>
	<section> <title>rmail with full addresses</title>
	  <para>
	    rmail is the oldest way to transfer mail to a remote system. 
	    However, today it is normally required to use addresses with
	    full domains for that (Well, they look like any normal address
	    for you, and we do not tell about the other way to not confuse
	    you ;). If you want this, you can use this transport:
	  </para>
	  <programlisting>
rmail:
    debug_print = "T: rmail for $pipe_addresses"
    driver=pipe
    command = uux - -r -a$sender_address -gC $domain_data!rmail $pipe_addresses
    return_fail_output
    user=uucp
    batch_max = 20
	  </programlisting>
	  <para>
	    However, all recipients are handled via the command line, so
	    you are discouraged to use it.
	  </para>
	</section>
	<section> <title>bsmtp/rsmtp</title>
	  <para>
	    This is a more efficient way to transfer mails. It works
	    like sending SMTP via a pipe, but instead of waiting for an
	    answer, the SMTP is just batched; from this is also the name
	    batched SMTP or short bsmtp.
	  </para>
	  <para>
	    Furthermore, this way won't fail on addresses like "
	    "@do.main. If you want this, please use this, if the remote
	    site uses rsmtp (e.g. is Exim 4):
	  </para>
	  <programlisting>
rsmtp:
    debug_print = "T: rsmtp for $pipe_addresses"
    driver=pipe
    command = /usr/bin/uux - -r -a$sender_address -gC $domain_data!rsmtp
    use_bsmtp
    return_fail_output
    user=uucp
    batch_max = 100
	  </programlisting>
	  <para>
	    and this if it wants bsmtp as the command:
	  </para>
	  <programlisting>
bsmtp:
    debug_print = "T: bsmtp for $pipe_addresses"
    driver=pipe
    command = /usr/bin/uux - -r -a$sender_address -gC $domain_data!bsmtp
    use_bsmtp
    return_fail_output
    user=uucp
    batch_max = 100
	  </programlisting>
	  <para>
	    Of course, these examples can be extended for e.g. 
	    compression (but you can also use ssh for compression, if
	    you want).
	  </para>
	</section>
	<section> <title>The router</title>
	  <para>
	    You need a router to tell Exim 4 which mails to forward to
	    UUCP. You can use this one; please adopt the last line. Of
	    course, it is also possible to send mail via more than one way.
	  </para>
	  <programlisting>
uucp_router:
    debug_print = "R: uucp_router for $local_part@$domain"
    driver=accept
    require_files = +/usr/bin/uux
    domains = wildlsearch;/etc/exim4/uucp
    transport = rsmtp
	  </programlisting>
	  <para>
	    The file <filename>/etc/exim4/uucp</filename> looks like:
	  </para>
	  <programlisting>
*.do.main       uucp.name.of.remote.side
	  </programlisting>
	</section>
	<section> <title>Speaking UUCP with the smarthost</title>
	  <para>
	    If you have a leaf system (i.e. all your mail not for your
	    local system goes to a single remote system), you can just
	    forward all non-local mail to the remote UUCP system. In
	    this case, you can replace "domains = ..." with "domains = ! 
	    +local_domains", but then you need also to replace
	    $domain_data in the transport by the UUCP-name of your
	    smarthost. The file <filename>/etc/exim4/uucp</filename> is
	    not needed in this case.
	  </para>
	</section>
      </section>
      <section>	<title>Receiving mail via UUCP</title>
	<section> <title>Allow UUCP to use any envelope address</title>
	  <para>
	    Depending how much you trust your local users, you might use
	    trusted_users and add uucp to it or use
	    local_sender_retain=true and local_from_check=false.
	  </para>
	</section>
	<section> <title>If you get batched smtp</title>
	  <para>
	    Allow uucp to execute rsmtp via
	    <programlisting>
commands        rmail rnews rsmtp
	    </programlisting>
	    in your <filename>/etc/uucp/sys</filename>, and ask the
	    sending site to use rsmtp (and not bsmtp) as the batched
	    command.
	  </para>
	</section>
      </section>
    </section>
    <section> <title>Notes on running SpamAssassin at SMTP time</title>
       <para>
         Exim can run
         <ulink url="https://spamassassin.apache.org/">
         SpamAssassin</ulink> while receiving a message by SMTP which
         allows one to avoid acceptance of spam messages. The Debian
         configuration contains some example code for running SpamAssassin,
         but like all filtering this needs to be handled carefully.
       </para>
       <para>
         SpamAssassin's default report should not be used in a add_header
         statement since it contains empty lines. (This triggers e.g.
         Amavis' warning "BAD HEADER SECTION, Improper folded header field
         made up entirely of whitespace".) This is a safe, terse alternative:
         <programlisting>
            clear_report_template
            report (_SCORE_ / _REQD_ requ) _TESTSSCORES(,)_ autolearn=_AUTOLEARN_
         </programlisting>
       </para>
       <para>
         Rejecting spam messages: Do not reject spam-messages received on
         (non-spam) mailing lists, this can/will cause auto-unsubscription.
         This also applies to messages received via forwarding services
         (e.g. @debian.org addresses). If theses messages are rejected the
         forwarding services will need to send a bounce address to the
         spammer and will probably disable the forwarding if it happens all
         the time. You will need to have some kind of whitelist to exclude
         these hosts.
       </para>
       <para>
         Security considerations: By default <command>spamd</command>
         runs as root and changes uid/gid to the requested user to run
         SpamAssassin. The example uses SpamAssassin default non-privileged
         user (nobody) which prevents use of Bayesian filtering since this
         requires persistent storage. You might want to setup a dedicated
         user for exim spam scanning and use that one, either for a separate
         SpamAssassin user profile or to run SpamAssassin as non-privileged
         user.
       </para>
    </section>
  </section>

  <section> <title>Updating from Exim 3</title>
    <para>
      If you use <command>exim4-config</command> from Debian, you will
      get the debconf based configuration scheme that is intended to
      cover the majority of cases.
    </para>
    <para>
      If <command>exim4-config</command> is installed while an Exim 3
      package is present on the system,
      <command>exim4-config</command> tries to parse the Exim 3 config
      file to determine the answers that were given to
      <command>eximconfig</command> on Exim 3 installation. These
      answers are then taken as default values for the debconf based
      configuration process. Be warned! <command>eximconfig</command>
      from the Exim 3 packages does not record the explicit answers
      given on Exim 3 configuration. So we have to guess the answers
      from the Exim 3 configuration file
      <filename>/etc/exim/exim.conf</filename>, which is bound to fail
      if the config file has been modified after using
      <command>eximconfig</command>.
    </para>
    <para>
      This is the reason why we refrained from doing a "silent update", but
      only use the guessed answers to get reasonable defaults for our
      debconf based configuration process.
    </para>
  </section>
  <section> <title>Misc Notes</title>
    <section> <title>PAM</title>
        <para>
	  On Debian systems the PAM modules run as the same user
	  as the calling program, so they cannot do anything you
	  could not do yourself, and in particular cannot access
	  <filename>/etc/shadow</filename> unless the user is in group
	  shadow. - If you want to use
	  <filename>/etc/shadow</filename> for Exim's SMTP AUTH you
	  will need to run exim as group shadow.  Only
	  exim4-daemon-heavy is linked against libpam. We suggest using
	  saslauthd instead.
        </para>
    </section>
    <section> <title>Account name restrictions</title>
        <para>
          In the default configuration, Exim cannot locally deliver
          mail to accounts which have capitals in their name. This is
          caused by the fact that Exim converts the local part of incoming
          mail to lower case before the comparison done by the
          check_local_user directive in routers is done.
        </para>
	<para>
          The router option caseful_local_part can be used to control
          this, and we decided not to set this option in the Debian
          configuration since it would be a rather big change to Exim's
          default behavior.
        </para>
    </section>
    <section> <title>No deliveries to root!</title>
        <para>
            No Exim 4 version released with any Debian OS can run
	    deliveries as root. If you don't redirect mail for root via
            <filename>/etc/aliases</filename> to a nonprivileged
            account, the mail will be delivered to
	    <filename>/var/mail/mail</filename> with permissions 0600 and
            owner mail:mail.
	</para>
	<para>
	    This redirection is done by the mail4root router which
            is last in the list and will thus catch mail for root that has not
            been taken care of earlier.
        </para>
    </section>
    <section> <title>Debugging maintainer and init scripts</title>
        <para>
	    Most of the scripts that come with this Debian package do a
	    <command>set -x</command> if invoked with the environment
	    variable EX4DEBUG defined and non-zero. This is particularly
	    handy if you need to debug the maintainer scripts that are
	    invoked during package installation. Since dpkg redirects
	    stdout of maintainer scripts, calling dpkg with EX4DEBUG
	    set might yield interesting results. If in doubt, invoke
	    the maintainer scripts with EX4DEBUG set manually directly
	    from the command line.
        </para>
    </section>
    <section> <title>SELinux</title>
        <para>
            There is no SELinux policy for Exim4 available so far.
	    Until this is resolved, users should use postfix or
	    sendmail if they intend to run SELinux.
        </para>
	<para>
	    The Debian Exim4 maintainers would appreciate if
            somebody could write an SELinux policy. We will gladly
	    use them in the Debian packages as long as there is
	    somebody available to test, debug and support.
	</para>
    </section>
    <section> <title>misc</title>
        <itemizedlist>
    	    <listitem>
    	        <simpara>
                    The charset for $header_foo expansions defaults to
		    UTF-8 instead of ISO-8859-1.
		</simpara>
	    </listitem>
    	    <listitem>
    	        <simpara>
		    <ulink url="http://marc.merlins.org/linux/exim/">
		    Marc Merlin's Exim 4 Page</ulink> has a lot of ACL
		    examples.
		</simpara>
	    </listitem>
    	    <listitem>
    	        <simpara>
		    For an example of Exim usage in a
		    <emphasis>large</emphasis> installation, see
		    Tony Finch's 
		    <ulink
url="http://www-uxsup.csx.cam.ac.uk/~fanf2/hermes/doc/talks/2005-02-eximconf/">
paper</ulink>
		    about the Exim installation at University of Cambridge:
		</simpara>
	    </listitem>
	</itemizedlist>
    </section>
  </section>  
  <section> <title>Debian modifications to the Exim source</title>
    <itemizedlist>
      <listitem>
        <simpara>
		Install the exim binary as /usr/sbin/exim4 instead of 
		/usr/sbin/exim-&lt;version&gt; with a symlink /usr/sbin/exim. Also
		adapt the documentation.
        </simpara>
      </listitem>
      <listitem>
        <simpara>
		Make the build reproducible. Pull date/time from debian/changelog
		and use it as build time instead of using __DATE__.
        </simpara>
      </listitem>
      <listitem>
        <simpara>
		Documentation updates
        </simpara>
        <itemizedlist>
	  <listitem>
            <simpara>
                  Mention how to install the Debian packaged perl-modules needed
                  for eximstats' graphs.
            </simpara>
	  </listitem>
	  <listitem>
	    <simpara>
		  Point to the <ulink
		  url="mailto:pkg-exim4-users@lists.alioth.debian.org">
		  Debian-specific mailing list</ulink> instead of
		  the <ulink url="mailto:exim-users@exim.org">official
		  exim-users list</ulink>.
	    </simpara>
	  </listitem>
	</itemizedlist>
      </listitem>
      <listitem>
        <simpara>
          <ulink
           url="http://marc.merlins.org/linux/exim/files/sa-exim-current/">localscan_dlopen.patch</ulink>:
		This patch makes it possible to use and switch between
		different local_scan
		functions without recompiling Exim. Use
		local_scan_path = /path/to/sharedobject to utilize
		local_scan() in <filename>/path/to/sharedobject</filename>.
        </simpara>
      </listitem>
    </itemizedlist>
  </section>

  <section> <title>Credits</title>
    <para><variablelist>
	<varlistentry>
	  <term><ulink url="mailto:aba@not.so.argh.org">Andreas
	      Barth</ulink></term>
	  <listitem>
	    <simpara>UUCP documentation</simpara>
	  </listitem>
	</varlistentry>
	<varlistentry>
	  <term>Dan Weber, Ryen Underwood</term>
	  <listitem>
	    <simpara>inetd/xinetd documentation</simpara>
	  </listitem>
	</varlistentry>
      </variablelist>
    </para>
  </section>

</article>
