How to Update GAL and OAB in Exchange 2010
What if your boss wants you to update the Global Address List and Offline Address Book in an Exchange environment. Yes, you could wait for Exchange to do it automatically (the default schedule is once a day) but what if you want to force the update immediately to reflect the changes on OAB?
Don’t worry, here comes PowerShell to the rescue :).
Use below Powerhsell commands in the same order:
Get-GlobalAddressList | Update-GlobalAddressList
So now that the GAL is updated. Now let's update the Offline Address Book (OAB).
Get-OfflineAddressBook “nameoftheofflineaddressbook” | Update-OfflineAddressBook
And last… when you update the OAB you’ll also need to inform Client Access Server that there is an updated OAB.
Get-ClientAccessServer | Update-FileDistributionService
Hope it helps!!!