LRich3001: I have not had any problems with autocomplete on email addresses in Mac OS X, the regular Mac Operating System Mail application. Just use "Window --> Previous Recipients" from the Mac Mail menu. This brings up a report of all your remembered email addresses. Once you delete them from this list, they will not appear during autocompletion as you type email addresses. Of course, if you retype one of them, they will be added back to that list. But you can always edit that recipient list.
MY PROBLEM is that iOS, the operating system for Apple mobile devices has no feature that allows you to edit the recipients list, from what I am being told on this community forum.
Apparently Apple users have been requesting this for years, since the invention of iOS, and Apple has not yet provided this feature. Also, it appears that Apple chooses to respond to user's requests with silence.