Oab exchange 2016 not updating
OABs in Exchange 2013 and later are improved over OABs in Exchange 2010.These changes were introduced in Exchange 2013: For OAB procedures, see Procedures for offline address books in Exchange Server.Renaming just a single or some of the files will result in an OAB corruption. A benefit of manually deleting the oab-file is that before they are being re-downloaded, you are working with the Online Address Book.
You could wait for Exchange to do it automatically (the default schedule is once a day) but what when you want to force the update to take place right now? This means that in the worst possible scenario, an update to the Address Book won’t become available to the user until 48 hours after the change.This situation however is extremely rare since the default maintenance time on Exchange is at AM and updates and downloads are usually performed during working hours.By default, a new installation of Exchange creates an OAB named Default Offline Address Book on the server.
This OAB is also the default OAB, which means it's the OAB that's used by mailboxes and mailbox databases that don't have an OAB assigned to them.
Full OAB download threshold To modify the threshold at which Outlook will download the full OAB rather than the incremental update, you can set the following Registry value Key: As the value, set at which relative size a full OAB download should take place rather than an incremental update.