match tickets without using Ticket# in subject ? (FollowUp)

[koki]

Hello,

I am using a software that uses a script to generate e-mails with custom X-OTRS-* headers to modify tickets.

the problem is, when i want to use X-OTRS-FollowUp-State: closed (successful), i need to send the e-mail with the ticket# in subject (or message body, if i enable it).
Also, i'm not sure if i have the option of passing the ticket# to the ticket generator.

Is placing the ticket# in subject of the mail the ONLY option for OTRS to match the new mail with an already existing ticket, and enter a followup state?

Thanks.

[koki]

Ideally, i am looking for a way to match tickets based on unique subject only, as i am able to ensure that every ticket will have an unique subject line.