Hi @alan gao ,
Are the problematic users from the new-installed servers? Or do they have some common attributes?
As I know, joining the DAG will not affect the using for Exchange server and Outlook client. So I think it should be the servers itself.
You could use the Test-OutlookConnectivity cmdlet to find if there are any messages:
Test-OutlookConnectivity "Outlook.Protocol\OutlookRpcDeepTestProbe\MDB1" -RunFromServerId Exchange2016 -MailboxId firstname.lastname@example.org | FL
Replace MDB1,Ex2016 and test@Company portal .com to the users'.
Or you can test it by EXRCA: https://testconnectivity.microsoft.com/tests/Ola/input
Also please try the following methods:
- Create a new mailbox from the new servers, or migrate the old, problematic users to other mailboxes/servers.
- Check the certificates, make sure it's using the right ones for both frontend and backend.
- Try logging in to OWA with these users.
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