Outlook NK2 Cache Rebuild
To rebuild a migrated mailbox's NK2 Cache which is Outlooks native auto complete use this free tool.
If you’re planning a mailbox migration which includes Outlook users, then you will need to rebuild the NK2 cache. Many users rely on their Outlook autocomplete and the NK2 cache is the file that provides this function
You type the first letters of a name (or e-mail address), and Outlook automatically proposes some matches. This works even if the text you entered doesn’t match any stored contact, user, or distribution list, but does match the name / email address of a past recipient. The NK2 cache constantly monitors and learns from your communications. In essence, Outlook automatically creates “virtual contacts”.
Again simply use this free tool