I spend today reading about how to pipe a mail received by postfix into a perl script. I read a lot but could hardly find a solution for my setup. So I give one here.

The case

An application must be able to process email coming in from the net and it must be also able to respond to these emails.

The setup:

• The machine is configured to send all emails over an MTA somewhere in the network
• The MTA hosts a virtual mail domain for which it forwards all its email to the machine
• The machine holds an application written in PERL
• A PERL script īs used as delivery agent to process some mails
• The tested platform: Linux Ubuntu 12.04 LTS, postfix 2.9.6

The postfix main.cf configuration created by dpkg-reconfigure postfix

    myhostname = [host name]
    alias_maps = hash:/etc/aliases
    alias_database = hash:/etc/aliases
    myorigin = /etc/mailname
    mydestination = [list for local delivery]
    relayhost = [the MTA name for sending emails]
    mynetworks = [see posfix documentation]
    mailbox_size_limit = [you would rather set it!]
    recipient_delimiter = +
    inet_interfaces = all
    inet_protocols = ipv4
    mail_spool_directory = /var/mail
[download]

My solution:

As usual TIMTOWTDI but a simple alias will NOT work! My solution works without:

• A cryptic central definition of a local delivery agent in master.cf
• Having pcre compiled in postfix. I have no use for this.
• Creating OS users or virtual users on the system.
• No other ugly things I read.

Now you have to:

• Modify your main.cf to redirect the mail.
• Create a redirect map for postfix
• Create an alias which will fool postfix and deliver the mail to the script

Modifications to the main.cf configuration

To avoid creating whatsoever users, we will use a kind of redirect. So we add a line like the following to the main.cf file:

Notice the hash: prefix to the file. This works well and avoid to re-compile postfix with pcre, in case it is not included.

Creation of the redirect map

Create the file defined above and enter a line with a regexp and a name in it:

Notice you have to use a regexp as first argument on this line! The alias name does not matter. Only secure name@domain is the correct email address.

Creation of the alias

Now we create the alias which will pipe the email into our script. Add a line like the following to the /etc/aliases file:

Notice you have to secure both alias name match!

Activate the whole thing

To activate all this you have to

• Create your redirect map with postmap [path to ]/redirect
• Activate your new aliases with newaliases
• Load the new posfix configuration with posfix reload

The result

This is what you will get in the STDIN of your script

   From [who ever]@[whatever].com  Mon Apr 22 17:48:08 2013
   Return-Path: <[who ever]@[whatever].com >
   X-Original-To: [name]@[machine domain]
   Delivered-To: [name]@[machine domain]
   Received: by [No matter to you]
   To: <[name]@[machine domain]>
   Subject: [What so ever]
   X-Mailer: mail (GNU Mailutils 2.2)
   Message-Id: <20130422154808.4100143A9@lap01>
   Date: Mon, 22 Apr 2013 17:48:08 +0200 (CEST)
   From: [who ever]@[whatever].com
   
   lkjahsdlfkjhlahsdf
   lkjahdsflkjhasdlfh
   lkjahsdflkjhsaldfhk
[download]

Notice: If you intent to open(OUT ">", $filename); in your PERL script it will fail with a missing privilege error. To avoid this you have to set default_privs = to an other user than nobody in the postfix main.cf. This has impact on the whole postfix setting. I did not analyse it until now. So if you do this, you do it at your own risk.

Enjoy!

K