Undeliverable mail" is mail that is OUTBOUND and not deliverable. It doesn't send you INBOUND mail that is to a non-existent address. If you want Brendan to get mail sent to mail@, then add that email address to his user account.
I don't know if you know what you are asking for, as far as having all misaddressed mail delivered to an account on your server. The sheer amount of spam you will get in whichever account you specify will surprise you. And when that misaddressed mail starts "sticking" to your server and not being bounced (which is the default behavior), then spammers will consider every email address in your domain a valid recipient and you will see the volume escalate rapidly....don't do it!
One thing I do (in a smaller business environment) is create email addresses for each user using all the most likely misspellings of their names. Plus addresses for anything else you might need, like nerds@ or sales@ or help@.
ShackDaddy
