To reset the whole Outlook nickname cache for Outlook 2010 and later versions, use one of the following methods:
Method 1
- Open Outlook.
- On the File tab, click Options.
- Click the Mail tab.
- Under Send Messages, click Empty Auto-Complete List.
- Click Yes.
Outlook will generate a new nickname cache.
Method 2
- Click Start, and then click Run.
- Start Outlook by using the /CleanAutoCompleteCache switch. To do this, type Outlook.exe /CleanAutoCompleteCache
Note If Outlook is not installed in the default location, you must point to the path of Outlook.exe.
Outlook will generate a new nickname cache.