@dirkdigs Thanks for reaching out.
You can follow this guide to perform a SMTP matching : https://support.microsoft.com/en-us/topic/how-to-use-smtp-matching-to-match-on-premises-user-accounts-to-office-365-user-accounts-for-directory-synchronization-75673b94-e1b8-8a9e-c413-ee5a2a1a6a78
There is a nice video as well explaining how to perform this : https://www.linkedin.com/pulse/learn-how-use-smtp-matching-match-on-premises-user-my-dileepa?trk=mp-reader-card
Hope this helps.
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