In OTRS, there is a tab labelled Admin.
Within that tab, there's a link called System Log.
When you receive a message, the logs will indicate things.
How do messages get created within OTRS for you? Is the OTRS mailbox a member of a mailing list and all tickets are generated from the mailing list? If you don't have loop check this is what happens:
1) user sends an email to mailing list
2) OTRS' mailbox receives the email
3) OTRS creates a ticket and sends an autoresponse to the mailing list
4) OTRS' mailbox receives the autoresponse
5) OTRS attaches the "Thank you for creating a ticket" to the ticket
6) If autofollowups are enabled, OTRS now sends a "I received your followup" to the mailing list
7) OTRS' mailbox receives the autofollow
8) OTRS attaches the followup to the ticket
9) go to 6
But without error messages and a way to replicate, I can't help you.