Test mail flow by validating your connectors in Exchange Online
To validate and troubleshoot mail flow from Microsoft 365 or 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 Microsoft 365 or Office 365 reaches:
Your organization's email server
A partner organization.
For more information, see Validate connectors
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.
Note
These tests replace Microsoft 365 or Office 365 mail flow troubleshooting that was previously available in the Remote Connectivity Analyzer.
See also
Configure mail flow using connectors
Set up connectors to route mail between Microsoft 365 or Office 365 and your own email servers