Author: Patrick von der Hagen Date: To: exim-users Subject: Re: [exim] using exim to reject prohibited mail to Mailman lists
atSMTP time
Chris Lightfoot said:
[...] > Unfortunately (and as with doing anti-spam testing at SMTP
> time) it is necessary to restrict each message transaction
> to exactly one list recipient. This is because permission
> to post to a mailing list is based on the From: header
> (and perhaps also Reply-To:), rather than the envelope
> sender. Obviously these values are known only after the
> DATA command. I have similar problems using other MLM-software and I'd like to add my
thoughts....
Currently I'm replacing listserv with symmpa. Mailman is of no interest
to me, because it is lacking too many features, e.g. active development
(for two years little more than bugfixes and an exiting roadmap for
mailman3 which hasn't been touched for ages...).
Listserv ist evil, sending thousands of bounces like "you are not a
member of the list", "mail has been forwarded to moderator", "mail has
been rejected by moderator", etc.
I'd like to reduce those bounces, so when incoming e-mail is processed
by exim, it checks whether the mailinglist would probably accept this
message and denies after data if it can be certain that the message
would be rejected. The setup is rather similar (but inferior) to the one
deveoped by Chris.
The moderation-messages should not be sent, but sadly Listserv has no
way to say "if SpamAssassin says it's probably spam, sent it to the
moderator quietly" and the moderator can not even suppress the message
"your mail has been rejected by the moderator".
Moving to sympa some things do change...
Sympa has a very sophisticated authentication-language to define how to
handle a message. The only reasonable way is not to check the
configuration yourself to decide how to handle a message, but to query
sympa and ask for a judgment.
Luckily it is very easy to use the sympa-perl-code, do some copy'n'paste
and create a Milter-daemon which can answer precisely how sympa will
handle the message. As has already been noted, such an attempt would be
a maintenance-nightmare, but I will to this at a
"proof-of-concept"-level, when I start to test exim's milter-support,
which Hilko Bengen is currently working at.
Given this milter and sympas capabilities, I expect to be able to reject
some messages during the SMTP-transaction and to suppress some bounces
like "forwarded to moderator" for Spam-messages having a high
SpamAssassin-Score.
Do you consider this to be worth the effort? Not just implementation and
maintenance of the code, but I'm worried about load as well. Currently
incoming mail is just dropped by MLM to an incoming queue and processed
when recourses are available, which wouldn't work with a
milter-interface anymore.
I really really want to reduce my bounces, not only because Spamcop
sometimes lists my mailinglist-server. But with mailinglists it is
awfully difficult. Any other ideas what could be done with reasonable
effort?
--
CU,
Patrick.
