This is a guide for clearing autocomplete in outlook this guide is the same for Outlook 2010 and Outlook 2013. There are 2 methods one is for an individual address. The other is for the whole Outlook profile. Generally you may be asked to clear the autocomplete if you get a bounceback and it is looking up wrong mail server

Clearing a single address

1 - Create an email in Outlook

2 - When you start typing an email address you will see a box come underneath. Press X. This will remove the autocomplete for this entry

Clearing all addresses

1 - In Outlook, go to File then Options
2 - Go to Mail. Scroll down to Send Messages then Empty Auto-Complete List
3 - Confirm the emptying of Auto-Complete then click Yes