At the moment if the "Forward" parameter is not specified and an error occurs when processing an e-mail, the mail is left in the mail box, as JIRA is "too scared" to delete the message.

This causes problems if the error occurs after an issue or comment has been created, for example, when attachments are processed, as the issue or message will be created every time the service runs.

Therefore, it is recommended to set the Forward paremeter. For more information see:
http://www.atlassian.com/software/jira/docs/latest/issue_creation_email.html

We need to find out how to deal with this case. Deleting a message feels like the wrong thing to do, as attachments could be important and were not processed correctly.

Ideas are welcome.