Debian Exim with Virtual Domains Pseudo-HOW-TO

Do not use exim in version 3 no more, for which this document is intended. Upgrade to a newer version of exim and use a different documentation, please.
This Pseudo-HOW-TO describes in short terms how to configure exim v3 with virtual e-mail domains and with a very simple list support.


What you need:

• A running installation of exim v3 (=> 3.20)

• Easy administration of virtual domain handling with exim in flat text files:
  
  • add one line in one file to open up a new virtual domain
  • one file per virtual domain holds its alias table
    
• Full domain aliasing
  
• Support for very basic mailing lists
• Fallback to defaults
  

• exim v3 (nano /etc/exim/exim.conf):
  
  1. Add the path /etc/exim/virtual_domains with the lsearch directive to the list of local domains (Option "local_domains"; the data is separated by colons, e.g. local_domains = lsearch;/etc/exim/virtual_domains : another.host.alias.tld).
     
  2. Download vdom_conf.part and open it in a text editor.
     
  3. Add the lines found in vdom_conf.part to the "Directors configuration" section. Insert them just before the "system_aliases" director in the exim configuration file.
     
     
• Files and Folders:
  
  1. mkdir /etc/exim/aliases.d
  2. mkdir /etc/exim/lists.d
  3. download aliases.default into /etc/exim
  4. download lists.default into /etc/exim
  5. download virtual_domains into /etc/exim

• Add the name of your virtual domain together with the name of the domain owner in
  
  /etc/exim/virtual_domains
  
  Each line in this file represents one virtual domain. A line is composed of two parts separated by a colon:
  
  <domainname> : <owner>
  (e.g. example.com : someuser)
  
  The domain owner must be a local mailbox or a simple list.
  
  

Advanced setup:

The following steps are all optional. Altough, if you omit to configure aliases and alike, you may only receive mails sent to the address <owner>@<virtualdomain> ; all other mails would get rejected (except the system-wide default addresses like postmaster, abuse, etc., see below).

• Optionally, you may define aliases for your domain. Create a new file named like your virtual domain in
  
  /etc/exim/aliases.d
  (e.g. /etc/exim/aliases.d/example.com)
  
  In this file, mappings may be set up:
  
  
  • Map a virtual user to a real user:
    To define to which local users mail will be delivered, use lines of the form
    
    sameuser : sameuser
    (Note: Both words are identical!)
    
    This line instructs the virtual_domain_to_local director to replace the domain part with the local system.
    
    E.g. On your system, there is a local user called "loc". She isn't the domain owner, but she wants to receive mails in the virtual domain "vdom.example". Set up an entry
    
    loc : loc
    
    This entry redirects mails addressed to "loc@vdom.example" to her local mailbox loc.
    (Note: You could achive the same by adding an entry of the form
    
    <virtual_user> : <local_user>@
    
    This way you wouldn't have to open an address in your virtual domain by the name of the local mailbox name).
    
    
  • Map virtual users to other virtual users or remote addresses:
    You may set up aliases in your virtual domain like the system aliases in /etc/aliases.
    
    <virtual_user> : <otheruser[@somedomain]>
    (e.g. softpatents : trash or frog : crap@swamp.example)
    
    
  • Implement a "catch all":
    Use an asterisks to implement a "catch all":
    
    * : <user>
    (e.g. * : frog)
    
    In this example, each mails that isn't aliased otherwise will be delivered to the user "frog".
    
    
• Optionally, set up system-wide defaults for virtual domains. RFC 822 requires the presence of a "postmaster" and "abuse" address, hence they are mapped per default to the owner. The file
  
  /etc/exim/aliases.default
  
  serves the defaults for all virtual domains and will be used for look-ups if domain specific alias processing failed. Normal mapping rules apply to this file.
  
  
• Optionally, create a simple mail distribution list. Create a new file named like the distribution list's address, including the local part, the @ sign and the domain part, in
  
  /etc/exim/lists.d
  (e.g. /etc/exim/lists.d/mylist@mydomain.com)
  
  Each line contains one address. If it's a local part only (no @ sign in the word), it gets qualified with the list address' domain part. For each address, a new mail is generated and delivered.
  
  Note: You just have to create the file to set up the list. You don't need an alias entry elsewhere!
  

• Use exim -bt <address> to test your setup. You may increase the verbosity level by adding the "-d <number>" switch. Refer to exim's man page (man exim).
• Send some mails, watch the headers and the server's log files.
  
  

• The described exim configuration is well tested, but may still contain bugs.
  
• Performance tests haven't been made at all. I assume it is suitable for small servers.

Other Exim3 Pseudo-How-Tos are available.