Certificate-primarily based connector configuration: Make sure that your on-premises email server is configured to use a certificate to deliver email to Microsoft 365, as well as Frequent-Title (CN) or Topic Alternate Name (SAN) while in the certificate is made up of a domain name that you've registered in Microsoft 365, https://fatallisto.com/story6705828/online-backup-storage-things-to-know-before-you-buy