Mailing List Message #14733
From: Bill Cole <>
Subject: Re: SMTP Delay
Date: Sun, 22 Aug 2004 17:18:04 -0400
To: SIMS Discussions <>
At 11:16 AM -0700 8/21/04, Warren Michelsen  imposed structure on a stream of electrons, yielding:
In the past, on this list, it's been suggested that having too many
RBL entries was causing too long a delay in accepting mail.

'too long' is so judgmental....

I note that an increasingly popular anti-spam tactic these days is
to add an SMTP Delay. Some server admins report a 40% drop in spam
with a 30-second delay. So...


Is this delay right at the very start, before accepting an initial
SMTP connection? Or is it just a delay after the connection is
established but before the mail is accepted -- like the delay
introduced by the use of too many RBLs?

Just about any delay works. The delay from SIMS doing a lot of DNSBL lookups is in a good place.

Either way, I'm wondering if I might be better off adding more RBLs
to my SIMS server. Will less patient spammers quickly give up and go

Yes, but you have to find ones worth using. There are hundreds out there, but some are very high-risk garbage.

Does SIMS in fact wait for responses from each RBL that is queried?

Yes. SIMS does not read from the connection for the HELO until it has checked all lists.

If so, I'm thinking that it might be possible to write a short delay
daemon that I can run on my OS X box, whose only purpose is to
respond to a RBL lookup with a not-blacklisted response -- after a
delay of 30 seconds.

That should work.

I then add the address of this daemon to my RBL list and thereby
implement a 30-second delay which SIMS is otherwise not capable of.
(Or would caching of responses cause this to fail?)

Is there a way to add a SMTP delay to SIMS or to achieve the same effect?


Will adding more RBL entries help to reduce spam (quite apart from
additional RBL hits) by introducing a delay?

Yes. I see scores of timeouts at that point every day even though I rarely take more than 10 seconds to respond to HELO.

Finally, will adding a delay just cause spammers to move more
quickly to secondary MXs for my domains?

They MIGHT try that, but the spammers who bother with secoondaries at all are going their first anyway...

Bill Cole

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