At least in smaller organizations, I've set up alternate spellings to forward to the correct one. In one company, for example, John Smith is firstname.lastname@example.org (hmmm, the kind of thing pageoneresults was talking about...). He periodically gets legitimate mail that the sender addressed to email@example.com, presumably sent by people who thought they recalled his address. I spotted some of these in the "catchall" mailbox. I finally just set "jsmith" and "johnsmith" to forward to the correct mailbox. End of problem.