Hello, we have setup the incoming mail fonction, and disabled the creation of new ticket:
When the ID in the subject is not recognized: 
  X	Reject E-mail
	Make new ticket
But if someone remove everything in the subject, it create a new ticket.
How could we fix this issue, without disabling all incoming email to reply to ticket.
thank you
EDIT:
i finally get it working by adding`:
Ignored subject filters (regular expressions): 
^((?!\[\[TI #).)*$
so i exlcude every email that didn't have our ticket id , and then if ticket id is wrong it's also ignored