SOLVED: How To Reset The Outlook Address Cache

If you are typing email addresses into your Outlook and they have gone wonky there are several things you can do but the easiest is likely just to flush the Outlook Address autocomplete cache.  In old versions of Outlook, that meant deleting the .NK2 file from %appdata%\Microsoft\Outlook however in Outlook 2016 (actually since Outlook 2010) your ‘nickname’ cache is stored in %localappdata%\Microsoft\Outlook\RoamCache

There are three easy ways to empty the Outlook Autocomplete Email Address Cache:

Flush The Outlook Email Address Cache Using File Manager:

1. Close Outlook
2. Using File Explorer, MY PC, THIS PC or whateva’, go to %localappdata%\Microsoft\Outlook\RoamCache
3. Delete Stream_Autocomplete_0_<long guid>.dat
4. Open Outlook
5. Have a nice day

Flush The Outlook Email Address Cache Using the Outlook GUI:

1. Open Outlook
2. Click FILE
3. Click OPTIONS
4. Click MAIL
5. Scroll down about half way and select EMPTY AUTOCOMPLETE button
6. Have a nice day

Flush The Outlook Email Address Cache Using Command Line:

1. outlook.exe /cleanautocompletecache
2. Have a nice day

If you have any questions, post them here or read:

1. https://www.slipstick.com/outlook/email/understanding-outlooks-autocomplete-cache-nk2/
2. https://grok.lsu.edu/article.aspx?articleid=18029