Imap updating cached messages
NK2 file from your hard drive, while Outlook 2010 and newer has a button to clear the Autocomplete cache in Options (screenshot below).
Beginning with Outlook 2010, Outlook does not use the NK2 file; it stores the autocomplete cache in the mailbox or data file and caches the addresses in an autocomplete stream at .
See Suggested Contacts and Auto-Complete Lists to learn more about Outlook 2010's autocomplete cache and suggested contacts.
Outlook 2010 also creates a contact for people you send mail to, as insurance if the autocomplete cache becomes corrupt.
Instructions are at Outlook doesn't save Autocomplete.
Outlook 2016, 2019, 365: DWORD: Max Nicknames Value: Between , in decimal The following registry files will change the registry key to 2000 entries.
Download the file for your version of Outlook and double click to run.
Clear the autocomplete cache using the File, Options, Mail, Empty Auto-complete list button.
You can also use the /cleanautocompletecache switch to clear the cache. Press Windows key R to open the Run command and type or paste the following line and press enter to start Outlook.