Throttling sendmail on *outbound* connections

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Author: Bill Jonas
Date:  
To: plug-discuss
Subject: Throttling sendmail on *outbound* connections
Hi all,

I've hit Google with different keyword combinations, read the list of
FEATURE()s and the FAQ on sendmail.org, and come up only with ways to
limit the inbound connection rate (either absolutely, based on system
load, or numbers of bad recipients).

Is there any way to limit the rate at which Sendmail *sends* email,
preferably on a per-domain basis? Someone I know had looked into it
before and said that he recalled coming to the conclusion that it could
not be done with Sendmail (although it was easily done with Postfix, but
that's not an option for this particular situation). Basically, an MX
server is stupidly rejecting email sent too rapidly with a permanent
error. One message to 25 recipients works fine, but 25 messages each to
a single (different) recipient will start failing (with a 550 error)
around message 15 or 20, requiring a wait of around five to ten minutes
before it will accept any more mail from the same host.

The admins of the remote system refuse to recognize that there is a
problem, even when presented with evidence (bounce messages). This is
Sendmail 8.11. Will I have to live with this, or is there a workaround?

-- 
Bill Jonas    *        *    http://www.billjonas.com/
"It's a dangerous business, Frodo, going out your front door.  You step
into the Road,  and if you don't keep your feet,  there  is  no knowing
where you might be swept off to."  --  Bilbo Baggins