The following are two articles on LWN about the mail transfer agents. The second would be available for free reading after September 7th, 2006.
A Comparision of Mail Transfer Agents - Part I
A Comparision of Mail Transfer Agents - PartII
What are the general expectations from an MTA?
Perform its primary task of sending mails. Should allow custom mail routes, sending via a SMTP server, envelope rewrite, virtual hosting.
Allow interfacing with spam and anti-virus utilities
Support authentication using the already existing authentication systems in my organization
Efficient mail storage (mbox is obsolete)
Support quotas
Easy to configure, help the […]