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  • From: Thomas Berry <address@concealed>
  • To: Patrick von der Hagen <address@concealed>
  • Cc: address@concealed, Richard Gilbert <address@concealed>
  • Subject: Re: [sympa-users] SMTP rate limiting
  • Date: Mon, 20 Oct 2008 13:31:44 -0700

  There was some discussion about providing sendmail instructions to make it work better with Sympa.

  Another good reason not to artificially slow Sympa's performance is that Sympa can only work on one outbound distribution at a time.  If a distribution takes several minutes for Sympa to create, any other messages received during that time are held in Sympa's distribution queue.

  We had this problem recently; the outbound sendmail configuration was making Sympa take several minutes to complete a distribution.  To improve sendmail's performance, I disabled sendmail's recipient canonify function.  Once disabled, Sympa was able to generate and hand over the messages to sendmail within a few seconds.   If we ever need to throttle the rate of distribution, sendmail's queue runner functionality would be used to do this, not Sympa.   I expect a similar method be available for Exim.

Patrick von der Hagen wrote:
Richard Gilbert schrieb:
We are using SYMPA 5.3.4 with Exim.  When a message is sent to all our
~30,000 users it gets sent out as fast as SYMPA can manage.  This has an
adverse effect on the two IMAP servers containing the users' mailboxes.
 I would like to be able to restrict the rate at which messages are sent
out.  I have reduced maxsmtp to 5 and nrcpt to 50 but SYMPA still
managed to send to all addresses in less than 3 minutes.

Can anyone suggest how I should do this?
Do it with exim. Don't do it with sympa.
Seriously, sympa has one known limitation about sending out messages: if
it is interupted while sending out messages, it has no track-report
about which recipients already had a copy sent out and it starts all
over again. Now, if you extend the period it takes sympa to send the
message to the MTA, you increase the risk of problems.

Exim has decent queue-handling, so there won't be such problems. You
would gain lots of flexibility, for example you could restrict the
sending-rate to your IMAP servers without slowing down messages to other

The smartest solution might be to solve the issue on your IMAP servers.
For example, if exim was the MTA on the IMAP servers, you could use
ratelimiting there, stop accepting messages when the load is above a
certain limit, etc.

But the way I suggest isn't really on topic on this list. ;-)

BTW, I'd just LOVE to seen an FAQ-entry "how to slow sympa down..." ;-)

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