This question already has an answer here:
I accidentally sent an email to a work colleague using a malformed email address and it bounced back. Unfortunately, even after sending email to the correct address, that old bogus one is still in the list (first) when I type his first name into the "To" field of an email.
...but his valid email address is the only entry I have in my Contacts, so that method doens't help.
Where is the bogus email address stored, and how can I expunge it?