[Dovecot] transitional weirdnesses

[Eric S. Johansson]

Mark E. Mallett explained:

> On Tue, Aug 19, 2003 at 06:49:03PM +0300, Timo Sirainen wrote:
> 
> I thought he was just musing about finding a delivery agent that

Mark, I know you're just being polite.  It's OK to say "grousing" or "whingeing" 
because that's what I was doing.  ;-)

> included a filtering language.  Not sure what good having such a thing
> in the IMAP server does, although I know some support it.  Seems to me
> that a facility to re-deliver mail or other general ways to give a
> message to a standalone tool (as briefly discussed a while ago) would
> be superior.

in all seriousness, what you are describing is the right place to put a filter 
as long as the user agent has a channel for notifications of mail delivery to 
different mailboxes.  Remember my grousing about complexity?  This kind of 
simplification is necessary.

So, to go to the next step, there are 4 components on the receive side of a mail 
system, MTA, LDA, MPA, MUA; mail transport agent, local delivery agent, mailbox 
presentation agent, and mail user agent.  Sendmail and postfix are examples of 
mail transport agents.  Procmail is an example of a local delivery agent. 
dovecot is an example of a mailbox presentation agent.  And Eudora, Mozilla, 
outlook are all examples of mail user agents.

if I understand you correctly Mark, you think that putting filter and plug-in 
facilities into the local delivery agent would be the appropriate place.  Please 
correct me if I'm wrong.

Architecturally, I consider putting the filter in the LDA appropriate because 
the filter operations happen at delivery time when it's appropriate not as you 
are trying to read your inbox.  It's also the appropriate place to put other 
types of processing such as antispam and antivirus checking.

One interesting thing about this model is that it implies if you can push mail 
around from the MPA, there is a question of whether or not you want to replicate 
LDA functionality in the MPA and if so, how much?  or how much common code can a 
LDA and MPA share?  Is there a different architectural structure where all 
inbound mail is injected through common path.

I don't expect anyone to do anything about this.  I'm just treading the ground 
to see what the terrain feels like.

---eric