Nigel Metheringham edited this page Nov 29, 2012 · 2 revisions

Q1002

Question

How well does Exim scale?

Answer

Although the author did not specifically set out to write a high- performance MTA, Exim does seem to be fairly efficient. The biggest server at the University of Cambridge (a large Sun box) goes over 100,000 deliveries per day on busy days (it has over 20,000 users). There was a report of a mailing list exploder that sometimes handles over 100,000 deliveries a day on a big Linux box, the record being 177,000 deliveries (791MB in total). Up to 13,000 deliveries an hour have been reported. These are quotes from some Exim users: "... Canada's largest internet provider, uses Exim on all of our mail machines, and we're absolutely delighted with it. It brought life back into one of our machines plagued with backlogs and high load averages. Here's just an example of how much email our largest mail server (quad SS1000) is seeing ... " [230,911 deliveries in a day: 4,475MB] "... Exim has to ... do gethostbyname()s and RBL lookups on all of the incoming mail servers, and he runs from inetd (TCP Wrappers connected). All the same, it seems to me that he runs as fast as lightning on our SCO 5.0.4 box (1 Pentium 166) - far faster than MMDF which I (and many customers) had before." "On a PII 400 with 128M of RAM running Linux 2.2.5, I have achieved 36656 messages per hour (outgoing unique messages and recipients). For about a 5 minute period, I was able to achieve an average of 30 messages per second (that would be 108000 m/hour)! We are using: (options that make a difference):

queue_only
split_spool_directory
queue_run_max = 1
remote_max_parallel = 1

We have a cron job hat runs every five minutes that spawns 5 exim -q if there are less that 120 exim processes currently running. We found that by manually controlling the concurrency of exim -q processes contending for the spool for remote_smtp delivery that we gained considerable performance - 10000 m/hour."


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