This may depend on what system you are using. I work with Domino (Lotus Notes). Also, a lot depends on the size and scope of your problem.
If you have one domain that gets used frequently in place of the correct one, you might set your system to accept EITHER domain as “good.” For instance, we have both “na.companyname.com” and “companyname.com” registered. Technically, the correct address is with “na” because we are in North America (without the “na” it’s our Global organization). However, since many people forget the “na,” our system accepts either one for our users. If your company used to be “gdc” and is now “fea” or if the two are divisions/subsidiaries or otherwise connected, you might want to simply have your servers accept either as an alias for the other.
On the other hand, if you only have a few people who might be getting mail to an alternative address (for instance, they’ve moved from one part of the organization to another, and it changed their domain), you might want to simply set those users up with the alias. In Domino this is child’s play — you simply list the address in the “user name” field of the Person Document in the Address Book. I’m not sure what you would need to do in another system, but that’s the basic idea.
As for saving the emails, well, that’s another issue entirely. There’s a lot of junk out there, and you could spend hundreds of hours trying to decide what is legitimate and what is simply spam. Our inbound SMTP servers used to hold undeliverable mail, but as spam got worse, this became impossible. Our mail filter provider now quarantines correctly addressed emails based on their anti-spam criteria and holds it for some period of time before dumping it, but the user has to know to go out there and look or call the Service Desk if they are missing something.
Also, remember that a bad address should fail back to the sender. If it’s really important to Jone that Ioan get that email, Jone should be able to find out that the address is bad, then call or at least double-check the address when it fails. If you capture and hold everything, Jone will never know the address is bad, will never correct it, and you will be forced to babysit your inbound emails forever.