Remove “ghost” email addresses from Apple’s Mail

When you create a new message in Apple’s Mail program, and start typing an address, the program tries to help by offering a list of suggestions. Pretty convenient unless the list has a bunch of old, and wrong, addresses.
The suggestion list is pulled from your Address Book and from previous emails you’ve sent. You can edit the list of Previous Recipients, remembered by Mail, by using this menu selection:

Mail-Previous Recipients