Ticket replies/follow ups creating new tickets?

[RagnaXBL]

Having an issue where customers replying to emails sent from otrs will create new tickets in the system instead of logging the email as a follow up to an existing open ticket. seems to happen regardless of what's inside the email subject?

[crythias]

This usually occurs with tickets created by email that are cc'd someone before the ticket is created, after which the cc'd person, who doesn't have the ticket number in the subject, replies all and the ticket is created.

After a while of this, it gets to a point where it's desired for all tickets to be created via web only. In that way, you can have the user give you the fields you need directly, and direct the tickets to their proper destination.