On Wed, 2007-02-07 at 09:36 -0500, Jarod Wilson wrote:
As for the performance issue someone else quoted regarding exim... At one point in time, I worked at a place that had lots of mail servers moving tens of millions of emails per day. There was no way in hell exim could handle the load (we tried). Both sendmail and qmail (ew) had their issues as well. Postfix was rock-solid, and had no problems holding up under the stress. Granted, this is a few years ago now, so postfix could have regressed (unlikely) and the others (save qmail) could have improved...
I've heard anecdotes the other way round too, and there are some very large deployments of Exim. I suspect that it depends a lot on how well-tuned it is. With large queues, you definitely need the 'split_spool_directory' option turned on to avoid putting too many files in a single directory -- it's going to suck quite hard otherwise; especially on older kernels. You may also want multiple queue-runner processes in parallel, if you have a large number of mails stuck on the queue that aren't immediately deliverable.