Zimbra zimlet

We need to create custom Zimbra zimlet which will automatically generate and add a reference number to the top of all outgoing messages from specisic mailbox Like : 2345-XXX If next user make new mail message from the same shared account it may looks like : 2346-PPP where digits equals to ascending number of the message form spesific mailbox and xxx and ppp eqauls to some users names who create this messages Ofcourse above Zimlet have to count all messages of specific