[otrs] Follow up based on number in email body

Hi All, We are logging calls with 3rd party and give them our OTRS Ticket number as a reference. They reply to us with this number in the body of their email, always with format of: Reference 1: *TicketNumber* I know I can use PostmasterFollowUpSearchInBody to scan the whole body but I was trying to use PostMaster filter instead (to ensure only their tickets are scanned). Do you know which Email Headers do I need to set up with *TicketNumber *to ensure the email is appended to the correct Ticket? -- Thank you Robert