Step-by-step guide

Clearing the cache, one entry at a time

1. Begin typing a person’s name and when the cached entry comes up, click the X on the right-side of the entry, as shown below.
   
   
   

   This will remove that entry from the auto-complete cache.  The next time you address a message to that person, their most current email address and display name will be added back to the cache. 

Clearing the entire auto-complete cache

If you have a lot of stale entries in the cache, you can clear them all at once using two different methods.

Method 1:

You can clear Outlooks auto-complete cache with a simple command. 

1. Close Outlook then click the Start button .
2. In the Search programs and files field type (or copy and paste): C:\Program Files (x86)\Microsoft Office\office15\outlook.exe /cleanautocompletechache, as shown below and press Enter.  This will open Outlook and simultaneously clear the cache.
   
   
   
   

Method 2:

In Outlook, go to File → Options → Mail.  Scroll to the Send Messages section and click Empty Auto-Complete List to clear every entry in the list.  The cache will start rebuilding itself as you send out new messages.