[Dovecot] New message notification

Hi

What is the best option to notify a user that a message has arrived? The intention is to write a script that connects to a jabber server and checks if the user is online, so then a message is sent to user notifying him that he has received a new message. The solution should be compatible with Sieve filtering, so the script should not be executed when the message is moved to the SPAM folder, or pass to the script an argument specifying the folder where the message has been saved.

Regards and thanks in advance.

Juan Asensio Sánchez - http://www.nutum.es