Message delivery Failure

Currently the company is reciving a lot of SPAM e-mail with the subject “undeliverable” this word have been added to the content filter and all messages with this subject are stop. (Great)
Sometime a genuine undeliverable message gets caught, which is not a problem if it’s spotted and forwarded on so the sender knows that there message failed.

I’m asking if the failed delivery message can be changed, so the it doesn’t have undeliverable as the subject? if so how do i do this?