[Mailman-Users] MS Exchange as a relay computer?

Ralf Hildebrandt Ralf.Hildebrandt at charite.de
Tue Jan 28 17:32:43 CET 2003

* alex wetmore <alex at phred.org>:

> Sorry for the misinformation.  I was going by some information that I
> learned on this list about two years ago stating that setting
> MAX_SMTP_RCPTS to between 5 and 10 will increase parallelism with the
> MTA.
> Will exim and postfix both open multiple connections to a remote
> domain when there are many recipients for that domain on a single
> message?

Postfix will group the recipients by domain (within certain limits, of
course) and then contact the domains MX and push down all the
recipients for - say hotmail.com - down this one pipe (one sender,
many recipients).

If there are MORE recipients than the limit allows, another connection
will be opened in parallel, but only if limits allow and the opposite
site is responsive. The number of parallel connections will increase
until a limit is reached or the other side becomes slow/unresponsive
(TCP slow start).

> The Mailman FAQ still recommends setting MAX_SMTP_RCPTS to 10 for
> performance reasons, but doesn't explain why.

This should definitely go!

Postfix uses:

default_recipient_limit = 10000
# max. of 10000 Recipients per single mail

smtp_destination_recipient_limit = $default_destination_recipient_limit
# max. number of recipients to be sent over smtp
# this should be increased for a mailing list server

And on the receiving side Postfix's smtpd accepts 1000 recipients.
Which should be increased for a mailing list server as well if you
inject via SMTP (which is fastest!)

Ralf Hildebrandt (Im Auftrag des Referat V a)   Ralf.Hildebrandt at charite.de
Charite Campus Mitte                            Tel.  +49 (0)30-450 570-155
Referat V a - Kommunikationsnetze -             Fax.  +49 (0)30-450 570-916
The trouble with being punctual is that people think you have nothing
more important to do.

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