Hi @Fenton, Mark ,
one exchange 2013 server on-prem, and one exchange 2016 hybrid VM.
To avoid misinterpreting your description, I would like to confirm with you whether Exchange 2013 and Exchange 2016 coexist in your environment and are not hybrid with Exchange Online.
If so, for the " An IIS directory entry couldn't be created " error on the on-premises server, you can refer to the following general troubleshooting steps:
- All Exchange servers are members of the Exchange Trusted Subsystems group.
- The Exchange Trusted Subsystems group belongs to the Administrators group for each Exchange server.
- The Exchange Trusted Subsystem group is a member of the Exchange Windows permission group.
- Start IIS Manager Navigate to -> Web Site -> Default Web Site Right-click Default Web Site and select Permissions Add Exchange Trusted Subsystem and grant Full Control to restart IIS Restart the Exchange server.
- 5.Check that the three default self-signed certificates are installed in all Exchange servers.
If the problem persists, feel free to post back and let's look for other solutions.
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