How to avoid mail loop?

[TonyGroves]

I'm writing a script to send an auto-response to each e-mail received into a user's mailbox when he/she is away, but am conscious of the need to avoid creating a mail loop. For example, if the auto-response message gets bounced, I don't want to issue another auto-response. However, I'm really stuck for ideas about how to handle this. I've thought about inserting a special header into each auto-response message, and checking for its presence before auto-responding again, but that doesn't sound very foolproof as the header might get stripped.

Does anybody know of any well-established simple but effective methods to tackle this problem?

Thanks a lot.

Tony.