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High Capacity Email

Horms (Simon Horman)
Senior Software Developer
VA Linux Systems

November 1999

``But Mr. Anderson, what good is a phone call if you can't speak.'' -Agent Smith, The Matrix


I would like to acknowledge the generous support of my former employer Zip World, and my current employer VA Linux Systems,, without whose help this paper would not have been possible. In particular, my colleague John Ferlito has been tirelessly patient and Felicity, who makes all things possible.


This paper is copyright 1999 Simon Horman and is released under the terms of the GNU General Public Licence, a copy of which is distributed with the source for this document.

Version Information

Version Date Description
1.0.0 20th June 1999 Initial Release
1.0.1 22nd June 1999 Minor Corrections
1.0.2 25th June 1999 Minor Corrections
1.0.3 20th November 1999 Minor Correction to Sendmail Regex Map
1.0.4 24th November 1999 Revised to include details of using layer 4 switching. Removed Performace data.
1.0.5 22nd December 1999 Minor Corrections. Reinserted diagrams.


Conference of Australian Linux Users (CALU)
9th-11th July 1999
Monash University

Linux World Expo
9th-12th August 1999
San Jose Convention Centre
San Jose
United States of America

The Bazaar
14th-16th December 1999
Jacob K. Javits Centre
New York
New York
United States of America

Linux Expo 2000
1st-3rd February 2000
Palais des Congrès


Email is one of the most well established and widely used services available on the Internet. With the popularity of Linux in the server market, especially amongst Internet Service Providers it should be no surprise that Linux is the platform of choice for many mail servers. The current growth of the Internet places increasing demands on both the hardware and software to deliver more mail to more users more quickly than ever before.

There comes a point where a single server can no longer cope. This is particularly a problem as the PC hardware market, which provides affordable hardware for applications such as this, is driven by increasing processor speeds and not the increases in I/O that are required to shuffle increasing volumes of mail.

One solution to this problem is to implement multiple email servers or a server farm to deal with the load. Messages are typically independent of each other and hence, parallelisation is a natural step to take. Implementing this is a manner that is transparent to users is non-trivial, but can can yield significant benefits, providing both increased capacity and high availability.

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