If you mean deleting from Mail's autofill, in Mail, go to Window>Previous Recipients and delete from there what you don't want any more. If you are asking something different, give us more info and we'll try to help.
If you mean deleting from Mail's autofill, in Mail, go to Window>Previous Recipients and delete from there what you don't want any more. If you are asking something different, give us more info and we'll try to help.