Written by Support InfoBridge
In case you have set up a hybrid Exchange Server environment with one or more Exchange On-premise instances and Exchange Online/Microsoft 365, there is a solution to use Exchange Online Synchronizer for all users. However, this can only work if your Exchange On-premise has Basic Authentication for EWS enabled. If you have enabled modern authentication for Exchange On-premise, you can't set up Exchange Online Synchronizer for the users from any of the Exchange On-premise instances. You are still able to set up Exchange Online Synchronizer for the users in Exchange Online/Microsoft 365 though.
We refer to this type of setup as 'mixed mode'.
Refer to the article Use the Synchronizer in mixed mode (OAuth and Basic authentication) on how to set this up.