Auto-merge - search in subject/raw does not seem to work?

[Sofia]

We need to find a way to auto-merge incoming new e-mails (which are each assigned new ticket-ID's by OTRS) from another ticket-tracking system.

For these incoming tickets, they have all the same sender (noreply@othersystem.org) and a ticketnumber in the subject and also in the body. The subject has three different lines: 'New servicechange', 'New ticket' and 'New responsible'.
When looking at the headers of the mail they don't containg much useful as only sender, subject and the usual is there.

I have been looking at the match-function, but not been able to figure out how to use it (I have never used regexp so I played around some but was not successful).

Is there a good way to auto-merge these? I was thinking about a general agent job as well but I guess I need some script or module to make it work and I don't have such.

We are marking our OTRS tickets with the other systems corresponding ticket ID as a freetext-field in the overview and I was hoping to find a way to match this and make new incoming e-mails to auto-merge to it as new articles.

As a work-around I tried to reply to one of these mails in OTRS to myself and then write back from Outlook and sending along all the e-mails for the ticket as attachments. Even if 'search in attachments' was switched on as well, OTRS does not seem to search and match any of the references I have configured (subject, attachments, raw). We have seen this for other e-mails as well, that new tickets does not get merged into existing tickets unless the ticketID is either in the subject or exists as a X-header in the e-mail.

I'm grateful for any inputs or ideas how to fix this.

Thanks in advance!