[Dovecot] problems with expire plugin

Hi all,

I'm experiencing problems to set-up the expire plugin in dovecot. This is the relevant part of my dovecot configuration

	dict {
	  expire = mysql:/etc/dovecot/dovecot-dict-expire.conf.ext
	}

	plugin {
	  expire = Trash 15 Junk 15
	  expire_dict = proxy::expire
	}

	protocol imap {
	  mail_plugins = quota zlib expire imap_quota
	}

File dovecot-dict-expire.conf.ext looks like:

	connect = host=127.0.0.1 dbname=virtual_email user=<user> password=<passw>
	map {
	  pattern = shared/expire/$user/$mailbox
	  table = virtual_expires
	  value_field = expire_stamp

	  fields {
	    username = $user
	    mailbox = $mailbox
	  }
	}

and the mysql schema for table virtual_expires is:
	+--------------+--------------+------+-----+---------+-------+
	| Field        | Type         | Null | Key | Default | Extra |
	+--------------+--------------+------+-----+---------+-------+
	| username     | varchar(75)  | NO   | PRI | NULL    |       |
	| mailbox      | varchar(255) | NO   | PRI | NULL    |       |
	| expire_stamp | int(11)      | NO   |     | NULL    |       |
	+--------------+--------------+------+-----+---------+-------+

However, when I delete any mail from the Inbox, the table is not updated, and there are no messages in the log, although mail_debug is set to "yes"

Does anybody has any idea on how to solve this issue?

Regards!

Felix