We run a moderated Mailman mailing list with ~1600 subscribers using
Exim as the MTA (of course!). One of my co-workers has observed a long
delay (~20 min I think) between his approving a post and the surge of
delivery reports in Exim's mainlog. I'm at a loss to explain this, but
another co-worker offered this theory:
> I'm pretty sure Exim has to wait until all the MX DNS lookups finish
> until it can start sending mail. This is the reason why qmail sends a
> separate message for each recipient instead of one per mail exchange.
> AFAIK, Exim has an option to do that as well. According to DJB, the
> bandwidth wasted by sending separate messages is not significant; it
> only pays if your messages are large and there are lots of users on the
> same exchange.
Are his assertions true? Ie., does Exim perform all 1600 MX DNS lookups
before starting to deliver mail? Can 1600 MX DNS lookups cause a 20 min
delay? (That seems possible if 1) our DNS cache [we use dnscache on
localhost] is not much help, and 2) Exim does all the MX DNS lookup
sequentially.) And does Exim have an option to send a separate message
to each recipient? If so, is its use advised in situations like this?
(These are not large messages, and there are 923 unique domains among
this list's 1618 subscribers.)
Thanks --
Greg
--
Greg Ward - software developer gward@???
MEMS Exchange http://www.mems-exchange.org
