Certificate-dependent connector configuration: Make sure that your on-premises email server is configured to employ a certificate to send out email to Microsoft 365, along with the Typical-Title (CN) or Subject Alternate Identify (SAN) from the certificate is made up of a domain identify that you've registered in Microsoft 365, and https://tinybookmarks.com/story17184968/new-step-by-step-map-for-azure-support