I’ve also run into the problem where the autocomplete will work within one session of Outlook, but the second you close it and open it again, the entries are all gone. If you have used Outlook for years, then your autocomplete database could be huge and if it suddenly stops working, it becomes a real pain to email someone! Sometimes autocomplete stops working because of problems with the PST file and other times it’s because of upgrading to a newer version of Outlook from previous versions. Note: If you are in a corporate environment, then technically your contacts are being stored in the cloud (Exchange server). Basically, every time you type in a name or an email address in Outlook, it stores this into a file and so the next time you type that name or email, it will autocomplete it for you. That is true for the autocomplete suggestion feature also. Nothing is stored in the cloud and therefore everything is based on local files.

Not so with Outlook 2016 or any previous version of Outlook. When you start typing a name or email address, it magically brings up all matching contacts! One of the great things about online email services like Gmail is that you never have to worry about things like autocomplete because all your contacts are stored in the cloud and Gmail automatically builds a giant index of everyone who has emailed you or everyone you have emailed.

Outlook 2013 autocomplete not working