dovecot - Jul 2003 - Hooks on folder operations

Hi all,

I'm interested in implementing an anti-spam system using bayesian
filtering. I had the idea of modifying and IMAP server to assist in
training the spam filter.

I was thinking of running a program whenever a message in moved to the
folder "Spam" or to a "Safe" folder. This could be easily
added to the
server as a generic feature, with hook programs for:
  * new message in a folder (either new, or moved into the folder)
  * message in folder is modified
  * message in folder is removed
and so on. If the support was generic enough there could be many uses
for it. Security of the external program needs to be considered but
doesn't really affect the IMAP server itself.

Anyway, if I were to write a patch to add support for running an
external program in these cases, would it be included? Any feedback
would be appreciated, if I'm going to do this I might as well do it in a
way that can be integrated back into the main tree!

Cheers
Grahame

-- 
Grahame Bowland                       Email: grahame at ucs.uwa.edu.au
University Communications Services    Phone: +61 8 9380 1175
The University of Western Australia     Fax: +61 8 9380 1109
                                     CRICOS: 00126G

Hi Grahame,
> Hi all,
> 
> I'm interested in implementing an anti-spam system using 
> bayesian filtering. I had the idea of modifying and IMAP 
> server to assist in training the spam filter.
Why do you want to hook it up into your imap server? I think it would be
better to prevent emails to enter the mailbox with the MTA rather than
removing it when the user is reading his email using imap.

Why? Because the spam that is in the mailbox might push the user over his
quota limit, and thus preventing legitimate emails to be delivered.
> I was thinking of running a program whenever a message in 
> moved to the folder "Spam" or to a "Safe" folder. This
could
> be easily added to the server as a generic feature, with hook 
> programs for:
>   * new message in a folder (either new, or moved into the folder)
>   * message in folder is modified
>   * message in folder is removed
> and so on. If the support was generic enough there could be 
> many uses for it. Security of the external program needs to 
> be considered but doesn't really affect the IMAP server itself.
With the new API code that Timo is making now, I guess this would be
possible.

(After all: if quota's are updated, something was written to the mailbox, or
deleted of course!)
> Anyway, if I were to write a patch to add support for running 
> an external program in these cases, would it be included? Any 
> feedback would be appreciated, if I'm going to do this I 
> might as well do it in a way that can be integrated back into 
> the main tree!
You can always build a plugin, and plugins can be loaded whenever an
administrator wants them to load. I don't know if Timo wants to include all
plugins that are / will be written for dovecot, but I guess there might be a
plugins part, where people can "post" their plugins so other people
can
benefit from them :)
> Cheers
> Grahame
Kind regards,

Maikel Verheijen
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On Wed, 2003-07-23 at 17:50, Maikel Verheijen wrote:
> > I'm interested in implementing an anti-spam system using 
> > bayesian filtering. I had the idea of modifying and IMAP 
> > server to assist in training the spam filter.
> Why do you want to hook it up into your imap server? I think it would
> be better to prevent emails to enter the mailbox with the MTA rather
> than removing it when the user is reading his email using imap.
> 
> Why? Because the spam that is in the mailbox might push the user over
> his quota limit, and thus preventing legitimate emails to be
> delivered.
Well, I'd actually want that too. I don't have quota problems and I make
spamassassin put all spam into spam mailbox. The few spams that go
through to inbox I usually just delete because I'm too lazy to make
spamassassin's bayesian filter to learn it. If I only had to move them
to spam mailbox, I'd probably do it :)
> With the new API code that Timo is making now, I guess this would be
> possible.
Yep.
> You can always build a plugin, and plugins can be loaded whenever an
> administrator wants them to load. I don't know if Timo wants to
> include all plugins that are / will be written for dovecot, but I
> guess there might be a plugins part, where people can "post"
their
> plugins so other people can benefit from them :)
I'll probably just add a plugins web page. Some of the most useful ones
I'll include in the tarball. Also I'll make it possible to compile the
plugins into the main binary so there's no overhead in dynamically
loading them.

At least quota and ACLs are going to be plugins. I'll make sure my APIs
are flexible enough to allow that.