Best Option for Account when User Leaves Company?

Hi,
Just wondering about the smartest way to handle email accounts when a user is no longer with a company?

I just checked a client's account, and there is one user who left a while back but their email is 65MB full. I'm guessing it's probably 90%+ spam, but I don't know if there are legitimate emails in there. I was going to have the client look through the account and keep any good emails while deleting the rest.

- But what should be done with the account after that?

If we just delete the account, wouldn't legitimate users just receive a generic bounce message? Probably not the best option.

If they set an autoresponder stating that the user was no longer with the company, wouldn't the email still be kept/stored?

What is the best protocol to use so that legitimate senders might at least know the person is not longer with the company (and that they may need to contact someone else), but not divert spammers to someone else's account?

Thanks!