I’m running a mailserver using Virtual Exim. This is a very cool way to manage mail users in a MySQL database. (for a very good HOWTO, try this link. Only in german! 🙁 )
It is really easy to add new domains, aliasdomains etc. all in a rather convinient PHP-based webinterface. As I startet hosting a few domains for some friends, they started asking for a way to get mails from other accounts and fetch it to their IMAP account on my server. I knew that fetchmail could do that. The downside is that fetchmail requires system users, which would make the whole Virtual Exim thing useless again.
So I decidet to hack my way throug vexim and look for a way to implement fetchmail in the vexim webinterface.

Outline of the whole idea:
Provide a form on the user-page in vexim, where the users could put in their fetchmail commands.
Save the individual fetchmail commands in seperate files in a subdirectory of the vexim installation.
Write a shell script that looks for all the files in the subdir and assemble them in a single file. Then call fetchmail and point it to this file.
Voila! fetchmail gets all the user’s mails and delivers it to their local mailboxes.

The following is my “quick & dirty” implementation:

1. First make a new subdirectory for the individual fetchmail files and make it writeable to the webserver process. (www-data on Debian)
   mkdir fetchmail chown www-data:www-data fetchmail
2. Then implement the new code in the userchange.php file of vexim at the apropriate place
   (I put it at the very end of the second form, right before the “Submit Profile” button but still in the PHP block)
   

   # Fetchmail Hack
   $datafile = "fetchmail/".$_SESSION['user_id'].".fm";
   if (file_exists($datafile)) {
       $output = join("",file($datafile));
       $output = stripslashes($output);
   }
   print "
   
   Fetchmail: ";
   print "Sample: 
   server  post.isp.net
   proto pop3
   user USERNAME-AT-YOUR-ISP is YOUR_ADRESS_HERE here
   password SECRET";
   print "{$output}";
   print "Caution: Mail will be fetched and immediately deleted from the remote server!
   Use the keep keyword if you do not want this.";
   # end fetchmail hack

3. Put the following in userchangesubmit.php right bevore "# Finally 'the rest' which is handled by the profile form"
   

   # Fetchmail Hack
   $file = "fetchmail/".$_SESSION['user_id'].".fm";
   if($_POST['fetchmail']){
       if(!$handle = fopen($file,"w")) {
           echo "couldn't open file ";
       }
       if(!fwrite ($handle, $_POST['fetchmail'])) {
           echo "couldn't write file ";
       }
       fclose ($handle);
   } else {
       unlink($file);
   }
   # end fetchmail hack

4. While editing this file I found a bug, which rendered all the form fields, except the two password fields at the top, on this page totally unusable.
   You have to find the following two lines:
   

   sa_tag={$_POST['sa_tag']},
   sa_refuse={$_POST['sa_refuse']},

   
   and change them to:
   sa_tag='{$_POST['sa_tag']}',
sa_refuse='{$_POST['sa_refuse']}',
   otherwise the SQL query will always return an error.

5. Now the last part:
   Save the following little shellscript, I named mine fetchme
   

   # #!/bin/bash
   
   # remove old file
   rm fetch_out
   
   # assembling file: fetch_out
   for file in /htdocs/vexim/fetchmail/* ; do
   cat $file >> fetch_out
   echo " " >> fetch_out
   echo " " >> fetch_out
   done
   
   # chmodding
   chmod 600 fetch_out
   
   # now fetching
   fetchmail -s -f fetch_out
   

6. Lastly you only have to fire up a cron job to run the script every five minutes or so.

Please feel free to comment and add enhancements.