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<chapter id="mail">
  <title>Electronic Mail</title>
  
  <para><emphasis>Rewritten by &a.jim;, 02 December 1999.  Original work
    done by &a.wlloyd;.</emphasis></para>

  <sect1>
    <title>Synopsis</title>

    <para>Electronic Mail, better known as email, is one of the most
      widely used forms of communication today. Millions of people use
      email every day, and chances are if you are reading this online,
      you fall into that category and probably even have more than one
      email address.</para>

    <para>Electronic Mail configuration is the subject of many <link
      linkend="bibliography">System Administration</link> books.  If you
      plan on doing anything beyond setting up one mailhost for your
      network, you need industrial strength help.</para>

    <para>Some parts of email configuration are controlled in the Domain
      Name System (DNS).  If you are going to run your own DNS server, be
      sure to read through the files in <filename>/etc/namedb</filename>
      and <command>man -k named</command>.</para>
  </sect1>

  <sect1 id="mail-using">
    <title>Using Electronic Mail</title>
    
    <para>There are five major parts involved in an email exchange.  They
      are: <link linkend="mail-mua">the user program</link>, <link
      linkend="mail-mta">the server daemon</link>, <link
      linkend="mail-dns">DNS</link>, <link linkend="mail-receive">a pop or
      IMAP daemon</link>, and of course, <link linkend="mail-host">the
      mailhost itself</link>.</para>

    <sect2 id="mail-mua">
      <title>The User Program</title>

      <para>This includes command line programs such as
        <application>mutt</application>, <application>pine</application>,
	<application>elm</application>, and
	<application>mail</application>, and GUI programs such as
	<application>balsa</application>,
	<application>xfmail</application> to name a few, and something
	more <quote>sophisticated</quote> like a WWW browser.  These
	programs simply pass off the email transactions to the local <link
	linkend="mail-host"><quote>mailhost</quote></link>, either by
	calling one of the <link linkend="mail-mta">server daemons</link>
	available or delivering it over TCP.</para>
    </sect2>
    
    <sect2 id="mail-mta">
      <title>Mailhost Server Daemon</title>

      <para>This is usually <application>sendmail</application> (by
        default with FreeBSD) or one of the other mail server daemons such
	as <application>qmail</application>,
	<application>postfix</application>, or
	<application>exim</application>.  There are others, but those are
	the most widely used.</para>

      <para>The server daemon usually has two functions&mdash;it looks
        after receiving incoming mail and delivers outgoing mail.  It does
	not allow you to connect to it via POP or IMAP to read your mail.
	You need an additional <link linkend="mail-receive">daemon</link>
	for that.</para>

      <para>Be aware that some older versions of
        <application>sendmail</application> have some serious security
	problems, however as long as you run a current version of it you
	should not have any problems.  As always, it is a good idea to
	stay up-to-date with any software you run.</para>
    </sect2>

    <sect2 id="mail-dns">
      <title>Email and DNS</title>

      <para>The Domain Name System (DNS) and its daemon
        <command>named</command> play a large role in the delivery of
	email.  In order to deliver mail from your site to another, the
	server daemon will look up the site in the DNS to determine the
	host that will receive mail for the destination.</para>

      <para>It works the same way when you have mail sent to you.  The DNS
        contains the database mapping hostname to an IP address, and a
	hostname to mailhost.  The IP address is specified in an A record.
	The MX (Mail eXchanger) record specifies the mailhost that will
	receive mail for you.  If you do not have an MX record for your
	hostname, the mail will be delivered directly to your host.</para>
    </sect2>

    <sect2 id="mail-receive">
      <title>Receiving Mail</title>

      <para>Receiving mail for your domain is done by the mail host.  It
        will collect mail sent to you and store it for reading or pickup.
	In order to pick the stored mail up, you will need to connect to
	the mail host.  This is done by either using POP or IMAP.  If you
	want to read mail directly on the mail host, then a POP or IMAP
	server is not needed.</para>

      <para>If you want to run a POP or IMAP server, there are two things
        you need to do:</para>

      <procedure>
        <step>
	  <para>Get a POP or IMAP daemon from the <ulink
	    url="../ports/mail.html">Ports Collection</ulink> and install
	    it on your system.</para>
	</step>

	<step>
	  <para>Modify <filename>/etc/inetd.conf</filename> to load the
	    POP or IMAP server.</para>
	</step>
      </procedure>
    </sect2>
    
    <sect2 id="mail-host">
      <title>The Mail Host</title>

      <para>The mail host is the name given to a server that is
        responsible for delivering and receiving mail for your host, and
	possibly your network.</para>
    </sect2>
  </sect1>
  
  <sect1 id="mail-trouble">
    <title>Troubleshooting</title>

    <para>Here are some frequently asked questions and answers.  These
      have been migrated from the <ulink url="../FAQ/">FAQ</ulink>.</para>

    <qandaset>
      <qandaentry>
        <question>
	<para>Why do I have to use the FQDN for hosts on my site?</para>
	</question>

	<answer>
	<para>You will probably find that the host is actually in a
	  different domain; for example, if you are in
	  <hostid role="fqdn">foo.bar.edu</hostid> and you wish to reach
	  a host called <hostid>mumble</hostid> in the <hostid
	  role="domainname">bar.edu</hostid> domain, you will have to
	  refer to it by the fully-qualified domain name, <hostid
	  role="fqdn">mumble.bar.edu</hostid>, instead of just
	  <hostid>mumble</hostid>.</para>

	<para>Traditionally, this was allowed by BSD BIND resolvers.
	  However the current version of <application>BIND</application>
	  that ships with FreeBSD no longer provides default abbreviations
	  for non-fully qualified domain names other than the domain you
	  are in. So an unqualified host <hostid>mumble</hostid> must
	  either be found as <hostid
	  role="fqdn">mumble.foo.bar.edu</hostid>, or it will be searched
	  for in the root domain.</para>
          
        <para>This is different from the previous behavior, where the
	  search continued across <hostid
	  role="domainname">mumble.bar.edu</hostid>, and <hostid
	  role="domainname">mumble.edu</hostid>. Have a look at RFC 1535
	  for why this was considered bad practice, or even a security
	  hole.</para>
          
        <para>As a good workaround, you can place the line:
          
          <programlisting>
search foo.bar.edu bar.edu</programlisting>
          
          instead of the previous:
          
          <programlisting>
domain foo.bar.edu</programlisting>
          
          into your <filename>/etc/resolv.conf</filename>.  However, make
	  sure that the search order does not go beyond the
	  <quote>boundary between local and public administration</quote>,
	  as RFC 1535 calls it.</para>
	</answer>
      </qandaentry>

      <qandaentry>
	<question>
	<para>Sendmail says <errorname>mail loops back to
	  myself</errorname></para>
	</question>

	<answer>
	<para>This is answered in the sendmail FAQ as follows:</para>
      
        <programlisting>
* I am getting <quote>Local configuration error</quote> messages, such as:

553 relay.domain.net config error: mail loops back to myself
554 &lt;user@domain.net&gt;... Local configuration error

How can I solve this problem?

You have asked mail to the domain (e.g., domain.net) to be
forwarded to a specific host (in this case, relay.domain.net)
by using an MX record, but the relay machine does not recognize
itself as domain.net. Add domain.net to /etc/sendmail.cw
(if you are using FEATURE(use_cw_file)) or add <quote>Cw domain.net</quote>
to /etc/sendmail.cf.</programlisting>
          
        <para>The sendmail FAQ is in
	  <filename>/usr/src/usr.sbin/sendmail</filename> and is
	  recommended reading if you want to do any
	  <quote>tweaking</quote> of your mail setup.</para>
	</answer>
      </qandaentry>

      <qandaentry>
        <question>
	<para>How can I do email with a dial-up PPP host?</para>
	</question>

	<answer>
	<para>You want to connect a FreeBSD box on a lan, to the
	  Internet.  The FreeBSD box will be a mail gateway for the lan.
	  The PPP connection is non-dedicated.</para>
          
	<para>There are at least two ways to do this.</para>
      
	<para>The other is to use UUCP.</para>
      
	<para>The key is to get a Internet site to provide secondary MX
	  service for your domain.  For example:</para>

	<programlisting>
bigco.com.            MX        10      bigco.com.
                      MX        20      smalliap.com.</programlisting>
          
	<para>Only one host should be specified as the final recipient
	  (add <literal>Cw bigco.com</literal> in
	  <filename>/etc/sendmail.cf</filename> on bigco.com).</para>
          
	<para>When the senders' <command>sendmail</command> is trying to
	  deliver the mail it will try to connect to you over the modem
	  link.  It will most likely time out because you are not online.
	  <command>sendmail</command> will automatically deliver it to the
	  secondary MX site, i.e., your Internet provider.  The secondary MX
	  site will try every
	  (<literal>sendmail_flags = -bd -q15m</literal> in
	  <filename>/etc/rc.conf</filename>) 15 minutes to connect to
	  your host to deliver the mail to the primary MX site.</para>
          
	<para>You might want to use something like this as a login
	  script.</para>

	<programlisting>
#!/bin/sh
# Put me in /usr/local/bin/pppbigco
( sleep 60 ; /usr/sbin/sendmail -q ) &amp;
/usr/sbin/ppp -direct pppbigco</programlisting>

	<para>If you are going to create a separate login script for a
	  user you could use <command>sendmail -qRbigco.com</command>
	  instead in the script above. This will force all mail in your
	  queue for bigco.com to be processed immediately.</para>
          
	<para>A further refinement of the situation is as follows.</para>
      
	<para>Message stolen from the &a.isp;.</para>

	<programlisting>
&gt; we provide the secondary MX for a customer. The customer connects to
&gt; our services several times a day automatically to get the mails to
&gt; his primary MX (We do not call his site when a mail for his domains
&gt; arrived). Our sendmail sends the mailqueue every 30 minutes. At the
&gt; moment he has to stay 30 minutes online to be sure that all mail is
&gt; gone to the primary MX.
&gt;
&gt; Is there a command that would initiate sendmail to send all the mails
&gt; now? The user has not root-privileges on our machine of course.

In the <quote>privacy flags</quote> section of sendmail.cf, there is a
definition Opgoaway,restrictqrun

Remove restrictqrun to allow non-root users to start the queue processing.
You might also like to rearrange the MXs. We are the 1st MX for our
customers like this, and we have defined:

# If we are the best MX for a host, try directly instead of generating
# local config error.
OwTrue

That way a remote site will deliver straight to you, without trying
the customer connection.  You then send to your customer.  Only works for
<quote>hosts</quote>, so you need to get your customer to name their mail
machine <quote>customer.com</quote> as well as
<quote>hostname.customer.com</quote> in the DNS.  Just put an A record in
the DNS for <quote>customer.com</quote>.</programlisting>
        </answer>
      </qandaentry>
    </qandaset>
  </sect1>
  
  <sect1 id="mail-advanced">
    <title>Advanced Topics</title>

    <para>The following section covers more involved topics such as mail
      configuration and setting up mail for your entire domain.</para>

    <sect2 id="mail-config">
      <title>Basic Configuration</title>
      
      <para>Out of the box, you should be able to send email to external
        hosts as long as you have set up
	<filename>/etc/resolv.conf</filename> or are running your own
	name server.  If you would like to have mail for your host
	delivered to that specific host, there are two methods:</para>

      <itemizedlist>
        <listitem>
          <para>Run your own name server and have your own domain.  For
	    example, <hostid
	    role="domainname">FreeBSD.org</hostid></para>
        </listitem>

        <listitem>
          <para>Get mail delivered directly to your host.  This is done by
	    delivering mail directly to the current DNS name for your
	    machine.  For example, <hostid
	    role="fqdn">example.FreeBSD.org</hostid>.</para>
        </listitem>
      </itemizedlist>

      <para>Regardless of which of the above you choose, in order to have
        mail delivered directly to your host, you must have a permanent
        (static) IP address (no dynamic PPP dial-up).  If you are behind a
        firewall, it must pass SMTP traffic on to you.  If you want to
        receive mail at your host itself, you need to be sure of one of two
        things:</para>

      <itemizedlist>
        <listitem>
          <para>Make sure that the MX record in your DNS points to your
	    host's IP address.</para>
        </listitem>

        <listitem>
          <para>Make sure there is no MX entry in your DNS for your
	    host.</para>
        </listitem>
      </itemizedlist>

      <para>Either of the above will allow you to receive mail directly at
        your host.</para>

      <para>Try this:</para>

      <screen>&prompt.root; <userinput>hostname</userinput>
example.FreeBSD.org
&prompt.root; <userinput>host example.FreeBSD.org</userinput>
example.FreeBSD.org has address 204.216.27.XX</screen>

      <para>If that is what you see, mail directly to
        <email>yourlogin@example.FreeBSD.org</email> should work without
        problems.</para>

      <para>If instead you see something like this:</para>

      <screen>&prompt.root; <userinput>host example.FreeBSD.org</userinput>
example.FreeBSD.org has address 204.216.27.XX
example.FreeBSD.org mail is handled (pri=10) by hub.FreeBSD.org</screen>

      <para>All mail sent to your host (<hostid
        role="fqdn">example.FreeBSD.org</hostid>) will end up being
	collected on <hostid>hub</hostid> under the same username instead
	of being sent directly to your host.</para>

      <para>The above information is handled by your DNS server.  The DNS
        record that carries mail routing information is the
        <emphasis>M</emphasis>ail e<emphasis>X</emphasis>change entry.  If
        no MX record exists, mail will be delivered directly to the host by
        way of its IP address.</para>

      <para>The MX entry for <hostid
        role="fqdn">freefall.FreeBSD.org</hostid> at one time looked like
        this:</para>

      <programlisting>
freefall		MX	30	mail.crl.net
freefall		MX	40	agora.rdrop.com
freefall		MX	10	freefall.FreeBSD.org
freefall		MX	20	who.cdrom.com</programlisting>

      <para>As you can see, <hostid>freefall</hostid> had many MX entries.
        The lowest MX number is the host that ends up receiving the mail in
        the end while the others will queue mail temporarily if
        <hostid>freefall</hostid> is busy or down.</para>

      <para>Alternate MX sites should have separate Internet connections
        from your own in order to be the most useful.  Your ISP or other
        friendly site should have no problem providing this service for
        you.</para>
    </sect2>

    <sect2 id="mail-domain">
      <title>Mail for your Domain</title>

      <para>In order to set up a <quote>mailhost</quote> (a.k.a., mail
        server) you need to have any mail sent to various workstations
	directed to it.  Basically, you want to <quote>hijack</quote> any
	mail for your domain (in this case <hostid
	role="fqdn">*.FreeBSD.org</hostid>) and divert it to your mail
	server so your users can check their mail via POP or directly on
	the server.</para>

      <para>To make life easiest, a user account with the same
        <emphasis>username</emphasis> should exist on both machines.  Use
	<command>adduser</command> to do this.</para>

      <para>The mailhost you will be using must be the designated mail
        exchange for each workstation on the network.  This is done in
	your DNS configuration like so:</para>

      <programlisting>
example.FreeBSD.org	A	204.216.27.XX		; Workstation
			MX	10 hub.FreeBSD.org	; Mailhost</programlisting>

      <para>This will redirect mail for the workstation to the mailhost no
        matter where the A record points.  The mail is sent to the MX
	host.</para>

      <para>You cannot do this yourself unless you are running a DNS
        server.  If you are not, or cannot, run your own DNS server, talk
	to your ISP or whoever does your DNS for you.</para>

      <para>If you're doing virtual email hosting, the following
        information will come in handy.  For the sake of an example, we
	will assume you have a customer with their own domain, in this
	case <hostid role="domainname">customer1.org</hostid> and you want
	all the mail for <hostid role="domainname">customer1.org</hostid>
	sent to your mailhost, which is named <hostid
	role="fqdn">mail.myhost.com</hostid>.  The entry in your DNS
	should look like this:</para>

      <programlisting>
customer1.org		MX	10	mail.myhost.com</programlisting>

      <para>You do <emphasis>not</emphasis> need an A record if you only
        want to handle email for the domain.</para>
	
      <note>
	<para>Be aware that this means pinging <hostid
	  role="domainname">customer1.org</hostid> will not work unless
	  an A record exists for it.</para>
      </note>

      <para>The last thing that you must do is tell
        <application>sendmail</application> on your mailhost what domains
	and/or hostnames it should be accepting mail for.  There are a few
	different ways this can be done.  Either of the following will
	work:</para>

      <itemizedlist>
        <listitem>
	  <para>Add the hosts to your
	  <filename>/etc/sendmail.cw</filename> file if you are using the
	  <literal>FEATURE(use_cw_file)</literal>.  If you are using
	  sendmail 8.10 or higher, the file is
	  <filename>/etc/mail/local-host-names</filename>.</para>
	</listitem>

	<listitem>
	  <para>Add a <literal>Cwyour.host.com</literal> line to your
	    <filename>/etc/sendmail.cf</filename> or
	    <filename>/etc/mail/sendmail.cf</filename> if you are using
	    sendmail 8.10 or higher.</para>
	</listitem>
      </itemizedlist>
    </sect2>
  </sect1>
</chapter>

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