Search, MailTips, and Free/Busy do not work for some Office 365 users

Last Updated: May 1, 2018

ISSUE

You may be unable to search or cannot see MailTips or Free/Busy.

When viewing Free/Busy you may see the error:

"No free/busy information could be retrieved. Your server location could not be determined."

This issue occurs on Build 8420.xxxx and higher. A recent Outlook 2016 change affects the User-Agent that causes problems with the Exchange EWSAllowOutlook feature.

The agent changed from:

User-Agent: Microsoft Office/16.0 (Windows NT 10.0; Microsoft Outlook 16.0.8201; Pro)

To:

User-Agent: Microsoft Office/16.0 (Windows NT 10.0; MAPI 16.0.8528; Pro)

Note: EWSAllowOutlook looks for "Microsoft Outlook" and not "MAPI". The effect with the Exchange server configured with EWSAllowOutlook will not allow Outlook to use EWS. This will present as a 403 error back to the client. This breaks EWS and REST.

This issue is fixed in Monthly Channel Version 1804 (Build 9226.2114) and higher. To get the latest update immediately, open Outlook and choose File > Office Account > Update Options > Update Now.

For Semi Annual Channel, the fix is estimated for May 8th 2018, in Builds 8431.2250 and higher. In the meantime, you can use the following workaround:

On the Exchange server use the below cmdlet to work around the problem:

Note: You will need to use PowerShell to run these commands. For more information, see Connect to Exchange Online PowerShell.

If the setting is per user, use this command: Set-CASMailbox user -EwsAllowList @{add="*MAPI*"}

To confirm the setting was applied, run this command: get-casmailbox user | fl *ews*
If the setting is at the organizational level, use this command: Set-OrganizationConfig -EwsAllowList @{add="*MAPI*"}

To confirm the setting was applied, run this command: get-organizationconfig | fl *ews*