Installing and Configuring Exim4

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  Configuring Exim4 and Courier IMAP under Debian GNU/Linux
  


  
  
  
  
  

2. Installing and Configuring Exim4
Installation of Exim4 from the latest Debian GNU/Linux packages is easy. The
installation is now based around debconf. If you are upgrading from a simple Exim3
configuration, you can use exim_convert4r4 to convert your configuration
file to the new format. If you used the previous
version of this guide, which covered Exim3, the conversion should succeed
without incident. I intend to discuss configuration via debconf, including
setting up local delivery to Maildir format, handling local domain email, and
configuring smarthosting for outbound email.
2.1. Installing and Configuring Exim4
Packages
First, install Exim4 using the standard and exciting Debian procedure you know
and love.

  jasonb@nebula:~$ su -nebula:~# apt-get updatenebula:~# apt-get install exim4

Fetching the meta package will result in the installation
of exim4-base,
exim4-config,
and exim4-daemon-light,
all version 4.34 as of this writing.
During installation, debconf will appear and ask you some
questions about your shiny new Exim4 installation. If you are upgrading From Exim3, your
configuration in /etc/exim/exim.conf will be parsed for appropriate
default values. If you intend to convert your existing Exim3 configuration,
you can go through the debconf screens, accepting the defaults, skip the rest of this
section. (If you haven't made many modifications to your old Exim3 configuration,
I encourage you to use the debconf generated configuration, as it's simpler.)
What follows is a discussion of each option presented by debconf. If you do
not walk through the debconfig
screens now or before continuing, the following discussion may not make much
sense. If you accidentally broke out of debconfig, you can always run the
following to restart the configuration process.

  nebula:~# dpkg-reconfigure exim4-config

For the duration of this guide I assume you have chosen to
use the monolithic configuration file, which is the default. Let's walk through
the debconf
questions on at a time.
First, if your host has a static IP address that is not
located in your ISP's dynamic range, you should be able to initiate SMTP
connections to remote sites directly and you do not need to use a smarthost. If
such is the case, select "internet site; mail is sent and received directly using SMTP".
For the rest of us, select "mail sent by smarthost; received via SMTP or fetchmail" as
your mail configuration. The system mail name should be your fully qualified
domain name. If you have not deployed DNS at your site, you may opt for using
your system's /etc/hosts file to give your host such a name as
demonstrated below. (If you choose the first option and you do not have DNS
configured, you will probably encounter difficulties receiving email.)

  nebula:~# cat >> /etc/hosts127.0.0.1    mail.example.com^D

Next, if the machine you are configuring is your only host,
you should accept the default address, 127.0.0.1, as the IP address to listen
on. If you intend to connect to Exim4 from other hosts, on the local network or elsewhere, you
should either include additional specific addresses for your mail host (e.g.
192.168.33.5), separated by a colon, or delete the suggested value and leave it
blank to have Exim4
listen on all available network interfaces.
Now, you need to decide what other destinations this host
is the final destination for. If you have no other hosts, you can leave this at
its default setting. If you have or intend to have an actual DNS domain across
your local network, enter that domain name here. Don't include any hostnames,
just the domain itself and its associated top level domain (TLD).
If you indicated your host will be sending and receiving
email directly, next you will be asked for which domains you wish to accept
email that are not considered local domains. Enter any appropriate domain names
that apply to your configuration. If you selected the smarthosting option
earlier, then you will not be prompted about which domains you which to relay
for.
Next, you are prompted for the address ranges for which
this mail host should accept connections for relaying mail elsewhere. For
example, for my local network I used the address range 192.168.33.0/24. Include
any additional ranges you want, separated by colons. Any hosts in the defined
ranges will be allowed to send mail off site. You most definitely want to
include hosts on your local network that you wish to send mail to the Internet
from.
Now, enter the address of the smarthost through which you
relay outgoing mail. Usually this will be your Internet service provider's
outbound SMTP server, the server you are probably using to send email from the
email client of your choice. You will not be prompted for a smarthost if you
have chosen to send and receive mail directly.
Finally, if you are using a smarthost to relay mail, you
can opt to have the outgoing address rewritten in the envelope header, if you
would prefer your mail appear to have originated from a fully Internet
connected host. Enter whatever fully qualified domain you would prefer, or
accept the default if you don't care.
Last, you will be asked if you wish to minimize the number
of DNS queries performed if you are in a dial-on-demand situation, perhaps with
a leased line with metered usage. Ordinarily you can select the default, which
is not to minimize DNS queries.
Upon completion of debconf configuration, your shiny new
configuration file will be placed in /var/lib/exim4/config.autogenerated.
As the filename implies, this is generated from your selections in /etc/exim4/update-exim4.conf.conf
and /etc/exim4/exim4.conf.template. Any changes to the actual
configuration, such as adding other routers or tweaking existing ones, must be
done in the latter file.
You can revisit the debconf configuration at any time by
running the following:

  nebula:~# dpkg-reconfigure exim4-config

2.2. Converting Your Exim3 Configuration
for Exim4
If you would rather recycle your old configuration using
the exim_convert4r4, read on. Otherwise, you can skip this section. If
you already configured Exim3 with support for delivering to Maildir style directories,
after the conversion you should be good to go. If not, you may wish to simply
go with the debconf
generated configuration discussed above, since it will be a lot easier to
enable Maildir style directories with that.

  nebula:~# cat /etc/exim/exim.conf | exim_convert4r4 > /etc/exim4/exim4.confRuntime configuration file converter for Exim release 4. ** The following comments describe problems that have been encountered   while converting an Exim 3 runtime file for Exim 4. More detail can   be found in the file doc/Exim4.upgrade. ** The receiver_try_verify option no longer exists, and has no equivalent   in Exim 4. ************************************************************ Please review the generated file carefully. ************************************************************

By default, if the file /etc/exim4/exim4.conf
exists, the Debian Exim4
initialization scripts will start the daemon using that configuration file and
ignore the file in /var/lib/exim4/config.autogenerated completely. If
you are happy with your converted configuration, you may wish to disable debconf management
of your configuration files entirely by editing /etc/exim4/update-exim4.conf.conf.

  # /etc/exim4/update-exim4.conf.conf## Edit this file and /etc/mailname by hand and execute update-exim4.conf# yourself or use 'dpkg-reconfigure exim4-config' dc_eximconfig_configtype='none'

Finally, restart the daemon.

  nebula:~# invoke-rc.d exim4 reloadReloading exim4 configuration files

2.3. Configuring Exim4 for Maildir
Delivery
Unlike configuring Exim3 for Maildir, the configuration for Exim4 is
straightforward. If you choose to use the debconf generated configuration file, you
need merely open /etc/exim4/update-exim4.conf.conf and make a single
edit. Add the option dc_localdelivery to the end of the file with
a value of maildir_home,
or change its value if it already exists, as shown below. (Future versions of debconf
configuration will likely include this as a configuration time option for the
Debian package of Exim4.)

  dc_localdelivery=maildir_home

Now, restart the daemon.

  nebula:~# invoke-rc.d exim4 reloadReloading exim4 configuration files

If you recycled a previous Exim3 configuration with Maildir
already configured, discussed above, then you need not do anything. You're
done.
2.4. Testing your new Exim4 configuration
It's important that your configuration work correctly
before proceeding further. Send yourself an email from another account
somewhere on the Internet, or from another user on your own machine. (root works for
this.) You might do the following:

  nebula:/home/jasonb# echo "my test" | mail -s "test message" jasonb

The purpose of this exercise is two fold. First, you'll
find out if Exim4
is configured properly. Second, and equally as important, Exim will create the
Maildir hierarchy in your home directory, ~/Maildir, which Courier IMAP craves
and requires to function. More on that later.

   nebula:~# tail -f /var/log/exim4/mainlog2004-09-14 16:58:00 1C7KNE-0006w8-NZ 2004-09-14 16:58:00 1C7KNE-0006w8-NZ => tester  R=local_user T=maildir_home2004-09-14 16:58:00 1C7KNE-0006w8-NZ Completed

Success!

   nebula:~# ls -ltr /home/tester/total 0drwx------  5 tester tester 120 Sep 14 16:57 Maildirnebula:~# ls -1 /home/tester/Maildir/new/home/tester/Maildir/new:1095195480.H806891P26670.nebula.internal.foo nebula:~# cat /home/tester/Maildir/new/1095195480.H806891P26670.nebula.internal.fooReturn-path: Envelope-to: tester@nebula.internal.fooDelivery-date: Tue, 14 Sep 2004 16:58:00 -0400Received: from root by nebula.internal.foo with local (Exim 4.34)        id 1C7KNE-0006w8-NZ        for tester@nebula.internal.foo; Tue, 14 Sep 2004 16:58:00 -0400To: tester@nebula.internal.fooSubject: testerMessage-Id: From: root Date: Tue, 14 Sep 2004 16:58:00 -0400 my test

You can see above Exim4 happily creates Maildir/
directory and sticks your new mail message in the Maildir/new/
directory.
It's necessary for each user to have this directory before Courier IMAP can
successfully access a user's mail, otherwise your mail client will return an
error. With that in mind, there are a few ways you can ensure that this
directory exists. For future users, you can modify your /etc/skel
directory and add a Maildir/ directory there. Thusly as root:

  maildirmake /etc/skel/Maildir

All future users will now have a Maildir/ with the
proper permissions and subdirectories. It's important to note that maildirmake
is only available after you install the courier-base package.
That still leaves existing users, though. You can mail
everyone on the system about the new IMAP setup and in doing so, Exim4 will create
the very Maildir structure you seek. Or you can write a script to add a Maildir
for each existing user with the maildirmake command like we did above
for /etc/skel. It's up to you.
You cannot proceed with the next step successfully, in any
case, without at least building a Maildir for yourself. So if you didn't send a
test message, run the following as your own user:

  tester@nebula:~$ cd ~tester@nebula:~$ maildirmake Maildir

2.5. Configuring New Mail
Notification
If you'd like to continue to receive the notification
"You have new
mail.", you need to modify several files.
First, /etc/login.defs. You will want to locate
the QMAIL_DIR and MAIL_FILE environment variables and
uncomment them. Then, comment out the MAIL_DIR environment
variable. The value of MAIL_FILE will be appended to the user's
home directory, such that the MAIL environment variable becomes
defined as MAIL=$HOME/$MAIL_FILE, which is what you want. An
example follows.

  QMAIL_DIR    Maildir/#MAIL_DIR    /var/mailMAIL_FILE    Maildir/

Second, modify your /etc/pam.d/login to receive
new mail notifications when you login on the console. Your /etc/pam.d/login
with the correction options for pam_mail.so should look like the
example below.

  session    optional   pam_mail.so standard noenv dir=~/Maildir

Last, you need to make a similar modification to /etc/pam.d/ssh
so you receive new mail notifications when you login via ssh. In order
for the MAIL environment variable to be set correctly, you must
ensure that the noenv is not passed to pam_mail.so.

  # Print the status of the user's mailbox upon successful login.session    optional     pam_mail.so standard dir=~/Maildir # [1]

Now you can enjoy mail notifications whenever you login to
your mail server.
2.6. Configuring Exim4 dot forward
Filtering
For a detail discussion of Exim's filter system, you should
check out Exim's
documentation
itself. For just the short of it, read on.
In order for Exim to recognize a .forward as
having Exim4
filter rules, the first non-whitespace entry must be:

  # Exim filter

Character case and anything following it on the same line
are ignored.
Next, you'll likely want some rules in your Exim4 filter .forward
file. Using a simple if
then elif else endif construct you can perform various tests
against each incoming email before delivery (or discarding) it to a specified
location. You can perform evaluations against any existing entry in an email's
header, like so:

  # Match any email who's To: header contains "exim"# and save it to .dir1if $h_to: contains "exim" then save Maildir/.dir1/ # Match email with a From: header that's# exactly "not@wanted.com" and save it to .SPAMelif $h_from: is "not@wanted.com" then save Maildir/.SPAM/ endif

To access the email header of your choice, append $header_,
or as abbreviated above, just $h_, to the full name of an email
header, following by a colon (:). The keywords is and contains are self explanatory. The save keyword, when
followed by a path that ends with a forward slash (/), will deliver the email
being evaluated in Maildir format. As such, the trailing slash is crucial.
Don't omit it.
In Courier's IMAP hierarchy, directories beneath the root
are dot directories. In addition, all subdirectories are denoted by periods,
not additional forward slashes. So, lists/Debian/User/ is actually .Lists.Debian.User/
on the filesystem and should be referred to in Exim filters as "save
Maildir/.Lists.Debian.User/" for things to be saved the way you
expect.
My own personal working Exim filter file looks like this:

  # Exim filter # Save yourselvesif error_message then finish endif # Let's make use of pipes# The script accepts input on STDIN and does stuff with the mailif $h_Subject: contains "uptime report"then       pipe "$home/bin/uptime.pl"endif # Handle mailing lists if $h_List-Id: contains "leaplist"  then save Maildir/.mailinglists.leap.linux/elif $h_from: contains "ebay.com"  then save Maildir/.Ebay/elif $h_Sender: contains "LINUX-L"  then save Maildir/.mailinglists.LUG/endif


  
  
  


  
  
  


               
               
               

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