Which mail tranfer agent (MTA) should I use? I generally recommend an underlying Unix host [explain], and there the possibilities include
Among exim's assets are its documentation, generally responsive and courteous (lead?) developer Philip Hazel, and active mailing list. On the other hand, exim is not a particular leader in regard to security.
Several people have told me exim's configuration is "easy", in contrast to that of, say, Zmailer, or qmail.
nullmailer is a queuing "dumb" MTA for machines which relay to one or more smarthosts. ... Its design is heavily influenced by qmail, and was created by its author for situations where a "mini-qmail" (queueless "dumb" qmail installation) was insufficient.
It's an excellent solution for workstations in a LAN environment, or for single Unix/Linux machines relaying to an ISP smarthost.
Correspondents have reported performance as much as three times as great as qmail's. In any case, both qmail and Postfix appear to be much zippier than Sendmail at high volume, although apparently no one has reproduced such results particularly rigorously.
While I haven't yet figured out how to backup a qmail configuration (the problem is that qmail works with inodes, so backing up as a file-system isn't effective), Dave Sill assures me that
Queue files are named after their i-node, but they're just normal files. Backing up the queue is easy using any of the standard utilities. The rub is restoring them. Luckily there are a couple utilities that'll munge a restored queue and rename the files properly. Pointers are on www.qmail.org (queue-fix, queue-rename).
Bennett Todd describes configuration for qmail, Postfix, and smail in a Usenet posting.
Along with the sites mentioned at www.qmail.org [explain], Blue Mountain Arts is a high-volume qmail user [explain].
... Dave Sill ...
Even old sendmail hands should read Frederick Avolio's review of Sendmail Pro.
Rumors have come my way that Smail maintenance is moribund. I haven't verified these myself.
A secure, effective and simple way of getting mail off a system to your mailhost. No suid-binaries or other dangerous things ...In the same vein, I often script little embedded MTAs with such languages as Tcl, Python, or Perl [explain details].
Warning: the above is all it does. It does not receive mail, expand aliases or manage a queue. . . .
The first serious attempt I know to bring modern security and performance concepts to bear on the current email environment was Zmailer ...Correspondents tell me that Zmailer is, in at least some high-volume situations, much the best performing MTA. CommuniGate Pro also makes strong claims about performance; so far, I've tested neither of these. My emotional reaction in regard to the former, at least, is skepticism, just because Zmailer is a monolith like sendmail.
Zmailer's in use at several high-profile sites. It handles Hotmail's inbound traffic.
Zmailer's a setuid monolith.