Test mail flow by validating your Office 365 connectors
To validate and troubleshoot mail flow from Office 365 to your organization's email server (also called on-premises server), validate your connectors. You can set up and validate connectors on the connectors page in the Exchange Admin Center (EAC). The built-in validation tests that your mail flow from Office 365 reaches:
Your organization's email server
A partner organization.
For more information, see Validate connectors in Office 365
Mail flow issues can also happen when your MX record is not setup correctly. To verify your MX record, see Find and fix issues after adding your domain or DNS records in Office 365.
These tests replace Office 365 mail flow troubleshooting that was previously available in the Remote Connectivity Analyzer.