Extension addresses (user-anything@domain) are a great way to create "disposable" adresses to give away with a great deal of confidence.
Later, when the shady website I gave my disposable address to starts feeding the spam circuit and the count starts to bother me, I can setup a filter in Zimbra and dispose of messages directed to that account as I see fit.
Zimbra allows all this, so far so good.
It would be even better to block the messages that we know are directed to a disposable account right at the SMTP "RCPT TO" stage. That would block them and not let them enter our Zimbra system at all.
I used to do this quite simply with the "relocated_maps" parameter in postfix. It allows the MTA to check a map and respond with a standard 5XX SMTP response that the user has relocated to another address. For example to relocate all my disposable, spammed addresses to !email@example.com or some other thing.
The relocated(5) page gives more info on the subject.
Any thoughts on this? Could something like this could be added to Zimbra (with UI, stats, the whole enchilada)?