we have the default trigger running for email on ticket creation.
Now we see sometimes the behavior if a customer has a stupid autoresponder a ping pong of emails.
The problem is caused by the autoresponder of the customer which just sends the same subject everything. Like thanks for your mail, without attaching anything from the old mail in subject or body, so zammad has no chance to assign it to a ticket.
Automatically generated ‘thank you for submitting your issue’ style tickets SHOULD set the Auto-Submitted header, which would cause Zammad not to send a response.