[Dovecot] Dovecot aspects of fighting spam
rainer.frey at inxmail.de
Tue Jun 1 17:45:51 EEST 2010
On Tuesday 01 June 2010 15:42:18 Phil Howard wrote:
> I see no documents in the Dovecot documents wiki on how Dovecot
> features can be used in the fight against spam. One hit came up in a
> search, and it was about how to fight spam in the MoinMoin Wiki itself
> (e.g. TextCHAs and such).
I guess you'll have the mental transfer of "fight spam" into "cause dovecot to
perform this and that action" yourself. The possible actions are, in general,
> I already asked in another thread about removing message files at the
> search from a designated "learn-spam" folder. My next question would
> be how to automatically place detected spam into a specific folder for
> the user to access or ignore as they deem fit.
You need to configure the MTA to accept and tag spam messages, e.g. with
Amavis D_PASS policy and appropriate tag levels. Then the most flexible way to
put the mails into a spam folder is to use the deliver plugin for sieve, which
can sort and filter mails depending on many different conditions, like
presence and/or value of any header. You can deploy a single system wide
default script for all users, which can be complemented or overwritten by
individual users (depending on configuration).
If you use dovecot 1.2, using the new Dovecot Sieve plugin is highly
recommended above the old CMUsieve.
The really recommended way nowadays is different though: *reject* as much spam
as possible in the MTA in the receiving SMTP dialog, with a combination of
blacklists, sender validation (e.g.DKIM), potentially greylisting (as you deem
appropriate) and lastly content scanning with s.th. like amavis+spamassassin.
I'd not expect a noticable amount of false positives, and in the rare cases
the sender will be notified. The false positives rate of users scanning
through a folder of tagged mail will be higher.
> A wiki document on how Dovecot helps (or how to help Dovecot) in the
> fight against spam, I think, would be helpful.
A howto-like page to describe the usage of some dovecot features in an anti-
spam context wouldn't hurt, OTOH there is not much anti-spam specific stuff at
all at the dovecot side.
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