[Dovecot] problems with expire plugin

[Felix Rubio Dalmau]

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