Outlook AutoComplete Cache Won’t Save
If Outlook’s autocomplete cache won’t save new addresses, the most likely cause is a corrupt entry in the cache. The fix, as one of my colleagues discovered, is to empty the autocomplete cache. In Outlook 2010 and 2013, open up the Options window. Under Mail, find the “Send messages” section and click on the “Empty Auto-Complete List” button. This will erase all saved email addresses from the cache, removing any that might be corrupt and preventing you from saving new addresses. Some people really love to use the cache as their address book, but that is a big mistake. There are too many things that can go wrong. If they really need to keep the addresses, use NK2Edit to export the cache to a csv file first. After you fix the problem, you can import that csv file into a new Contacts folder in Outlook. Don’t re-import it back to the cache, though. You might just re-import the same problem again.