Gal is not updating
In that case, you can completely reset it by deleting the files making up the OAB or by recreating your mail profile.
Check whether Outlook and the computer can access the Offline Address Book file on the server.
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If the issue isn't resolved, proceed to the next step. To do this, ensure that you can view any changes in the GAL by using Microsoft Outlook Web App.
If the expected changes aren't present in the GAL, the changes will not replicate to the Offline Address Book.
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NOTE: If you change your on-premises Active Directory schema, but the Microsoft Azure Active Directory Sync Tool still doesn't synchronize these changes correctly, go to this Microsoft website to continue troubleshooting this issue: Troubleshoot directory synchronization Manually download the Offline Address Book in Outlook.