[otrs] OTRS PostMaster Filter and Ticket Updates

Hi All, My scenario is like this. I created a ticket in OTRS and after that If I'm going to receive any updates to that ticket by POP3 POstmaster, I want to create a post master filter where it adds the email as a note to the exisiting ticket rather than creating a new ticket for that. One of the OTRS members said that this will be possible if we have ticket number in the subject line but didnt said much about the Post Master filter creation. Can some one please let me know what are the rules I need to define to achieve this . HOW SHOULD THE POST MASTER FILTER SHOULD BE?? Thanks Siva Prasad