MX Server

With the additional load from virus / spam filtering effecting the performance of our core mail servers, we decided to create an MX server to place in front of our current mail system. This server is designed to receive all incoming mail for our domains, and pass them off to our primary mail server. The server is also designed to accept outgoing messages to prevent users from distributing viruses.

Some of the requirements we established:
1.) Quick processing, mail cannot queue longer then a few seconds. Remove load from current mail server.
2.) Detailed accounting, we need to know exactly why messages get blocked.
3.) Management, we need to be able to quickly add additional domains without complicated configuration. Release messages from queue which need delivered.

MailScanner
The solution we found which works best is Mail Scanner. Mail Scanner is an application which gives us the ability to integrate a number of application (SpamAssassin / ClamAV, etc) to give each message a complete score. This allows for use to run each message through multiple scans before eventually passing the message off to the primary mail server. This application gave us part of the solution, but didn’t offer the detailed accounting which we were looking for.

This is where Mail Watch comes into play.

Mail Watch is probably the most exciting piece of the configuration. It’s given us detailed accounting information, and lets us generate reports to get an idea on who is abusing our mail system. I would highly recommend this application package to anyone who is using Mail Scanner but wants to add an easy to use interface for quick accounting.

Some of the additional tweaks we’ve made include:

1.) Leaving the incoming queue in memory rather then writing it to the drive. This seems to speed up the scanning process tremendously.
2.) Purging the MySQL accounting data every quarter to keep database queries quick.

As we continue to grow we will likely add two MX servers balancing via DNS. We currently process around 20,000 messages per day on our Dual Xeon 1.8Ghz server with 2GB RAM, running a RAID 1 Mirror. The extra MX server should add some additional reliability as well.

So far the MX server has worked prefectly. We could not be happier. Special thanks to everyone who helped make this project come together.