Monitoring Benefit
The Mail Flow check verifies that a message can be sent from and delivered to the system mailbox on the monitored server — an end-to-end test of the transport pipeline rather than a check that a service is running.
Services can be started, queues can be empty, and mail can still not move. This test is what catches that.
How do we verify the monitoring test results?
1. Run the same test Exchange runs. From the Exchange Management Shell on the affected server:
Test-Mailflow2. If it fails, check the arbitration mailboxes first. This is the single most common cause, and it is easy to confirm:
Set-ADServerSettings -ViewEntireForest $true
Get-Mailbox -Arbitration | Format-Table Name, ServerName, Database, AdminDisplayVersionSupported versions of Exchange 2016 and 2019 should return seven arbitration mailboxes, five of which are System Mailboxes. The System Mailboxes are required for Test-Mailflow to report success. If any are missing, the test will fail even though ordinary user mail is flowing perfectly well.
3. Distinguish a monitoring failure from a mail failure. If Test-Mailflow fails but users are sending and receiving normally, the fault is very likely in the arbitration mailboxes or the test's own path, not in transport. Check whether anyone is actually affected before escalating it as a mail outage.
Common warning or error results, and potential solutions
| Result | Potential solution |
| Failed status, users unaffected | Check the arbitration mailboxes as above. Missing System Mailboxes cause this exact pattern. Microsoft documents how to re-create them. |
| Failed status, users also affected | A genuine transport problem. Check the transport services and the queues on the affected server before looking at the test itself. |
| Failure appeared after a migration or database move | Arbitration mailboxes may have been left on a decommissioned server or in a dismounted database. The Get-Mailbox -Arbitration output above shows where each one currently lives. |
| Intermittent failures | Often latency rather than breakage — the test message is arriving, but not within the expected window. Check queue lengths and server load at the times it failed. |
| Results are stale rather than failing | If several unrelated checks stopped updating at the same moment, look at the ENow SQL database connection rather than at Exchange. |
Monitoring page. The detail behind this indicator is served by the ENow web server at:
http://localhost:20080/MailscapeWeb/MailFlow.aspx?server=<SERVER>Replace localhost with the web server's host name if you are browsing from elsewhere, 20080 with your own port if it was changed at installation, and <SERVER> with the monitored server you are investigating.
Reference. Test-Mailflow and Re-create arbitration mailboxes.
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