[Sysadmin] Come on then... decision time

[David Kaufman]

William Anderson wrote:
> David Kaufman wrote:
>> i'd avoid Exim because, although it's the debian default MTA and
>> i've used it and found it completely suitable for routine system
>> mail, i have read that in several places that, being a monolithic
>> process (it doesn't spawn children to handle the incoming
>> connections), exim has lower performance and more problems when it
>> encounters high loads, large numbers of concurrent connections, and
>> "plugin-style" virus and spam filters, all of which we'd expect to
>> have with l.e.o.
>
> exim doesn't use a "monolithic" process style if you don't want it to
> - just have it called by xinetd and it will happily spawn extra
> processes to handle load.

> Can you prove this "lower performance" claim?

certainly not.  i've just followed some threads (mostly on the
debian-devel and debian-isp mailing lists) and was merely repeating what
i heard with no actual proof or, as i mentioned, personal experience to
offer.  in fact, both of these lists exhibit regular, recurring flame
wars over the "which is better, exim or postfix?" question.

the only "data" i have seen is:
http://www.dt.e-technik.uni-dortmund.de/~ma/postfix/bench2.html

which compares qmail, postfix and exim, and finds that (on freebsd)
qmail and exim cannot come close to postfix without the use of freebsd's
softupdates (a disk caching system that is considered unsafe for mail
systems, since it reports to applications that files were written to
disk before they actually have been).  unfortunately this link also
somewhat outdated and, i think slanted towards postfix by someone trying
to justify their use of it.

> What problems does it have with high load, large numbers of
> connections?
>
> What do you see as a problem with "plugin-style" filtering?
> Spamassassin and clamav play very nicely with exim, probably
> more so due to the transport mechanism it uses.

again, i didn't mean to sound like any sort of expert -- i remember
reading both that high connection volumes and the spawning of spam/virus
filter programs were being reported as exim's "problems" when i was
doing research on MTA's for our work systems, and since our mail servers
both accept a high volume of automated, machine-generated messages, and
then spawn external programs to process them, i chose to go with
Postfix.

with Postfix being the default MTA on Mandrake and Suse, and Exim the
default on Debian, there is plenty of religious zeal on both sides of
the debate.  i think my decision was somewhat swayed by the exim FAQ
itself: http://www.exim.org/exim-html-4.30/doc/html/FAQ.html#TOC273
which states that "the author did not specifically set out to write a
high- performance MTA", and that
http://www.exim.org/exim-html-4.30/doc/html/FAQ.html#TOC271 "Exim was
not designed for handling large queues"

but actually, i've been googling this morning for more specific
information and coming to the conclusion that the more serious Exim
performance limitations that i was finding reports of were pre-2002
(Exim3) and have been resolved with version 4.

so i apologize for spreading unsubstantiated FUD about exim, and revise
my reasons for voting for postfix to simply these: i know it better, and
am more comfortable with it.

-dave