[Mailman-Users] Mailman/Exim problem with very slow outgoing mail on one list

[Stephanie]

I'm hoping someone has some ideas for fixing a problem with very
slowwwww outgoing mail delivery for one particular list I host.  I'm
running Mailman 2.1.5 and Exim 4.40.  I host a couple dozen Mailman
lists on my Linux server, most are less than 300 members except for
one list with about 1,100 members, about 850 set to individual emails
and 250 on digest.

I've hosted this list (call it ABC list) for almost two years now and
up until about a month ago, outgoing mail for ABC list (and all other
outgoing mail, list) got processed very quickly, getting delivered to
the recipient's server at a rate of about 1,000-1,200 per hour.  The
ABC list will get posts in several messages, usually two to four per
topic and once a month, there's a posting that's 12 to 14 messages.

About a month ago, at a time where there were NO updates to anything
on my server, hadn't been any for about two weeks prior, suddenly
outgoing mail on the ABC list *only* slowed down to a quarter of the
usual speed, processing about 300 messages per hour, even if there
were no other messages in the Exim queue.  The messages get processed
by Mailman to Exim at the usual speed, takes about ten minutes for
Exim to accept 850 messages and queue them and start delivering them
but instead of being sent out 1,000-1,200 per hour, suddenly they
stick in Exim, even ones for delivery to local email addresses,
delivering only about 300 per hour.

All other lists and private mail process at the normal faster levels. 
If there's outgoing messages from other Mailman lists, those messages
will get processed and sent out while the messages for ABC list
languish in the Exim queue.  (Note: most all of the lists I host, and
especially the busier ones, including ABC list, are set in Mailman to
VERP all messages, it's been set like that for over a year.)  Forcing
additional Exim queue runners doesn't do anything but increase the
load on my server as it tries to process even more very slow messages.

About two weeks ago, one of my users created a new list (call it XYZ
list) and directly added about 950 users in one go (she was creating a
backup list for Yahoogroup) and she neglected to turn off the notices
to the listowner of new members and she didn't turn off the welcome
message either so approximately 1,900 messages got sent out
immediately.  At the same time, there were about 10,000 messages in
the Exim queue for ABC list (the 12 part monthly posting), processing
at their very slow pace.  The individual welcome messages and new
members for XYZ list notices flew right on past, the 950+ welcome
messages and the new member notices went thru the Exim queue in about
20 minutes with just a handful left waiting on problems at the
recipient's server.

At first glance I would think this is strictly an Exim problem but
since it's affecting a single Mailman list, I keep coming back to
something going wrong between the two.  I have checked Exim logs and
Mailman logs, can't see anything out of place.  I've gone thru the
Mailman FAQ and also the Exim/Mailman HowTo and tweaked things but
still no difference, every other list flies on by while the ABC list
plods along slowly.

This problem applies to all the outgoing messages on the ABC list,
doesn't matter what receiving ISP, they all get treated just a slowly.
 I've checked that in the logs and watched it in the queue, even
messages destined for other users I host will sit and wait.  I've
watched the individual delivery attempts, when I force delivery of one
of the ABC list messages, it'll take at least 30 seconds before Exim
even attempts to lookup the recipient's ISP but once it gets to that
point, it flies right on thru, speedy as usual.  It's that 30-45
second delay as it's pulling up the message (or whatever) that I can't
determine the cause.  If it was all mail or even all Mailman mail, I'd
know it was some problem with Exim or dns (which I checked and changed
anyway, didn't make any difference) but it's just this one list, no
other lists and other non-list mail is not affected at all.

The only thing I can think of that I haven't tried yet is exporting
all the list settings and member list (there's no archives thankfully)
and deleting the list and re-creating it but I have no idea if that
would help...any suggestions, hints, tips, wild ideas, anything at
all, is very welcome.

-- 
hth,
Stephanie

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