[Dovecot] Question: email system architecture

[Gland Vador]

Hi,

I have a question about how to implement a mail system, but I don't know 
where to ask.

Until now, I have a mail system who receive mail by postfix and 
transport it through procmail to the /var/spool/mail/username mailbox. 
 From here it is retrieved through dovecot (POP3).

Now I have two more users, I want to implement a IMAP server, and also 
provide a webmail (squirrelmail) interface. And in order to filter spam, 
I want to install spamassassin. Until now it was thunderbird who made 
the filterring, but with a webmail interface it's no more possible.

So suppose that I have configured procmail to deliver "good" mail in an 
Inbox folder and "spam" in a SPAM folder. This for each user mailbox.
I also have configured dovecot as IMAP server and any IMAP client can 
see the two folder with spam and ham.

And here comes my implementation problem. If a user see a "good" mail in 
his spam folder (or vice-versa) he will take this mail and move to his 
inbox folder. But, I want to be able to say to spamassassin to learn 
that this message is ham, with the command sa-learn, and also remove the 
x-spam* headers. And I don't see a good way to do that.

In my opinion, it should be the MUA task, but spamassassin is server 
based. It's any way that dovecot when it moves the mail between tho 
folders can call an external script who will make this job in fonction 
of source/destination folder?

Maybe it's a silly question (I don't know IMAP and his possibilities). 
In this case, can anyone explain (or point to) me a way to do that ?

Sorry for this long message.

Edd.