Allow Reply to Unknown Users for Mail Handlers

Overview

In the current mail handler system, if you uncheck the "Create Users" box, the system will silently ignore any incoming messages from unknown addresses. It would be beneficial to be able to configure a reply message to let the sender know that their ticket wasn't created.

Our Use Case

We recently we rolled out new email addresses for a segment of our user-base. Since we're OnDemand, we can't use Crowd or integrate with our AD environment, so needed each profile to be touched individually to update the addresses, and there were enough users affected that we had to rely on the users to update their own. Unfortunately, users who failed to update their profile were not courteous enough to stop emailing our helpdesk, and each request got bounced by the system without informing the users that there was an issue.

Additional Requirements

In addition to just a configurable email, we should be able to black or whitelist domains to reply to. This is important for people running web-accessible instances, since spam-bots and other undesirables will latch onto a reply and go nuts.