We had a problem where M365 users could not retreive Free/Busy information from on-premise Exchange server. Hybrid setup was run and everything was working fine except this. After research I found out that TargetSharingEpr is the way to look at. There are many sites out there that are pointing to the same setting but only Set-OrganizationRelationship is used to change the value. The problem is, this value is available for two commands: Set-IntraOrganizationConnector Set-OrganizationRelationship While we changed the value in Set-OrganizationRelationship it didn't work until we changed the value in Set-IntraOrganizationConnector too. By default it should work with just TargetAutodiscoverEpr but for us it didn't. Finally we ran this command on Intra Organization Connector which is used from Cloud to On-prem: Set-IntraOrganizationConnector -TargetSharingEpr https://mail.domain.com/ews/exchange.asmx And it worked.
If you have a problem with Microsoft Teams not showing Calendar for users that have on-prem mailbox then you missed some of the steps in making a hybrid. To be honest, sometimes it is not very easy and clear what exactly you have to do. In my setup I am running Exchange 2019 on Windows 2019 server. 1 . First step is to run Microsoft Office Hybrid Configuration Wizard This step is necessary even if you ran AD Connect and selected Exchange Hybrid. Go through the Wizard and when you finish, it will tell you you need to configure OATH manually as it is not part of the Wizard (in year 2020) 2. Follow all the steps on https://docs.microsoft.com/en-us/exchange/configure-oauth-authentication-between-exchange-and-exchange-online-organizations-exchange-2013-help For me step 8. was not necessary as I am running Exchange 2019. After successful implementation of OATH connection Calendar will be immediately available to Teams users. Test connection with: ON-PREM Ex