We have a lead who unsubscribed from our emails yet he keeps receiving them. He is not found in our Lead Database or in our Salesforce database. Is there any other way he could still be subscribed, and if so how do I make sure he really is unsubscribed?
Maybe instead of searching for his email address in your lead database search for his first and last name, he might have subscribed with a different email address that is forwarding emails onto another address.
A long shot but I can't see any other reson he would be receiving your emails if he doesn't even exist as a lead in your database.
Often we find this to be the case of an email being forwarded, as Cathal has suggested. The person might not even know that his previous co-worker's emails are being forwarded to him, for example.
If they can forward you the email, you might be able to work through a process of elimination to determine the correct email address that should be unsubscribed.
I've seen several instances of the case that Dory suggested where a previous coworker's email is sent the their inbox. You can generally track these down with a smart list of Company Name and Was Sent Email, to identify records from the same company. Alternate company names, subsidiaries, and email domains can make the process of finding the record a bit trickier, however.