Sendmail vs Postfix vs Qmail vs Exim

We have choice in using MTA in linux. We can use sendmail, postfix, qmail or exim. The selection of MTA depends on many factor such as followings

* a good security record
* performance on high load
* flexible and easy to understand configuration files
* interact with databases in many formats
* can speak many of the SMTP variants in use
* quality third-party documentation is available
* there are significant user communities

Let us start with qmail(http://www.qmail.org/)

Security: Good record
Performance: Excellent
Out Since: 1996

Books are available for configuration, Not very simple to configure because it simply redesign the unix mail system concept. But the most important point is this software is not maintained and morever qmail is not purely a open source solution.

Postfix (http://www.postfix.org/) is like qmail but interface is like unix so easy to configure. postfix sits between qmail and exim.Postfix is less versatile than Exim, and this is largely due to its foremost design criteria being security. Personally in love postfix.

Security: Good record.
Performance: Excellent
Out Since: 1997
Community: Medium-sized 

Now sendmail(http://www.sendmail.org/). Sendmail is accused of many security loopholes in past. Now its a bit improved. Sendmail shipped as default MTA is many linux distro. Its easy to configure and suitable is enviroment where security is not top priority. Sendmail is most well known MTA

Security: Not good but still better from past versions
Out since: 1982
Performance: Ok for many
Community: Large 

Exim(http://www.exim.org/) is not very secure. Exim has its own filter language and very well documented.

Out since: 1995
Security: Quite good
Performance: Very good
Community: Large