Is there any way I can force a manual update of the Offline Address Book (OAB) in Outlook or reset it completely otherwise?
In general, Outlook will automatically update the Offline Address Book (OAB) for Exchange accounts once every 24 hours.
While in Offline mode you will have to enter the full email address for any recipient that isn't saved in your contacts list.
After completing these steps, you can reopen Outlook, make sure that it is not in Offline mode, and search for an email address to confirm that it is now referencing the most current global address book.
The quickest and most thorough method is to simply rename the If you are still having issues with your OAB afterwards or if the files aren’t being recreated after a manual update, it is very likely that your OAB issues are rooted deeper in your mail profile.
In that case, it is recommended to recreate your mail profile.
You can disable the option “Download changes since last Send/Receive” to make sure you get a complete fresh copy of the OAB but this could take longer to download.