Tech Tip: Exporting MS Exchange 5.5 users to Postfix

I've been using the Postfix mail system for some time, and a handful of customers are using it as a front end (with SpamAssassin) to MS Exchange. In these cases, the Postfix system only does relay, not final delivery, and the usual way to configure relay is to simply pass everything that comes in the door for the domain to the mail server for that domain.

The problem arises for invalid addresses (old users, typos, etc.). Postfix accepts the mail from the outside, but when it tries to deliver it to Exchange, the recipient is rejected as unknown. This puts the burden on Postfix to deliver a bounce to the sender (who just as often as not is unknown).

Here it behooves us to somehow teach Postfix about the valid users inside so it won't accept this bogus mail in the first place: no need to deliver any bounces. it can be maintained by hand, but this only works for very small and static operations, and even then it gets tiring. Better is to automate it.

With my friend Steve Gardiner we have built a system that automatically exports the user email list from the Exchange directory, conveys it to the Postfix mail system, and rebuilds the relay_recipients file automatically. Running this from WinAt (the command scheduler), it becomes a fully unattended system requiring very little ongoing maintenance.

I've written a Tech Tip to describe the process:

• Tech Tip: Exporting MS Exchange 5.5 Users to Postfix
  

Posted by Steve at May 19, 2003 02:35 PM | TrackBack