What is a Milter?
Sendmail and Postfix are the most popular open-source mail transfer agent (MTA); Sendmail has both free and commercial editions.
Due to the emergence of threats and unwanted content such as viruses and spam, a need arose to filter those messages closer to the perimeter, before they reach the end-user mailbox; however, since both Sendmail and Postfix were designed as MTAs, they lack the ability to perform content analysis of the messages passing through, thus enabling only basic RBL (Real-time Blackhole List) IP lookup.
In order to solve this problem, content-scanning software such as Amavis and Mail-Scanner were developed. The integration of that software requires strong skills in Linux and Postfix configuration; also, the flow of the message in these tools isn’t optimized and wastes resources:
- The message is accepted by the MTA
- The message is forwarded to the content scanner (Amavis, etc)
- The content scanner executes external software (such as ClamAV, SpamAssassin, etc.) in order to scan the message
- The clean message is forwarded to a 2nd copy of the MTA
- The 2nd MTA delivers the clean message
In version 8.12, Sendmail introduces an API, called the “Sendmail Content Management API” (a.k.a. Sendmail Milter); This API enabled the ability to inter-connect third-party content analysis software and have them analyze the mail messages at their arrival time (in real time). It actually enabled the examination and modification of the message content and meta-information during the SMTP transaction. The API enabled interconnection with more than one software.
Following Sendmail’s success, in their 2.4 version, Postfix has enabled full compatibility support to Sendmail’s milter.
Bottom line: it’s finally possible to add anti-virus and anti-spam milters to filter out messages easily and efficiently.
The Commtouch Milter
Commtouch has introduced a Milter that enables the use of Commtouch Anti-Spam, Zero-hour Virus Outbreak Protection and GlobalView Mail Reputation with Sendmail or Postfix MTAs.
The goal in offering the Milter is not only to provide superior technology for our partners but also to ease the integration process, and to allow partners to benefit from Commtouch’s added value without having to invest too many additional resources.
This is why Commtouch has initiated its integration tools strategy that allows partners to leverage existing security infrastructures to improve competitive offerings. As part of this initiative Commtouch has already released its Commtouch Plug-in for SpamAssassin, and now we are proud to release the Commtouch Milter Plug-in. Like other Commtouch offerings, it is primarily targeted at security vendors and service providers (including hosting providers, ISPs, etc.) that are servicing over 5000 mailboxes. Of course, it can also handle carrier grade offerings of tens of millions of mailboxes.
Why Milter? Why Now?
It is true; even before we offered the Milter, it was possible to integrate our SpamAssassin plug-in and have it scanning your messages without changing your current topology too much, whether you use spamd-milter, Amavis, Mail-Scanner or any other content-scanner/milter that integrates SpamAssassin.
But is it good enough? That’s a rhetorical question! SpamAssassin uses a lot of resources, and in order to enjoy the best performance, you are much better off taking SpamAssassin out of the equation.
The Commtouch Milter provides the best way to integrate a content analysis mechanism with your Sendmail or Postfix MTA, enjoying best performance, minimum latency and proper usage of Commtouch’s technologies and services.
If you want to learn more about Commtouch Integration Tools in general or about Commtouch Milter solution in particular, please visit http://www.commtouch.com/commtouch-milter-messaging-security, or even better – download our free evaluation software of the Commtouch Milter.