Use accepted domains to enroll, manage, and create users in multiple domains under a single cloud-based organization.

Running Exchange Server 2003 or later in your on-premises organization? You may be able to extend many on-premises Exchange features into your cloud-based mailboxes.

You can use CNAME records to let Outlook clients connect by using the Autodiscover service.

Use SPF records to help prevent spoofing and phishing.

A faulty DNS record can cause connectivity or mail routing issues. Use the Exchange Remote Connectivity Analyzer (ExRCA) to troubleshoot.