I'm bringing this issue up again as we just got another call from a user who wanted to get rid of the old email addresses in the drop-down when composing a new message.
The bottom line is there's no need for a separate address book that's buried under Settings->Advanced Settings->Auto-complete. If a user wants addresses to show up in auto-complete, simply add them to Contacts.
Hoping this can be fixed in SM 16 as it's been Under Consideration for ~2 years:
https://portal.smartertools.com/community/a744/disable-auto-complete.aspx
Thanks!