Certificate-centered connector configuration: Be sure that your on-premises email server is configured to make use of a certificate to send out email to Microsoft 365, along with the Typical-Title (CN) or Subject matter Alternate Identify (SAN) from the certificate includes a domain name that you've got registered in Microsoft 365, https://tinybookmarks.com/story17187280/the-smart-trick-of-directadmin-migration-that-no-one-is-discussing