1. Home
  2. Sensors
  3. Mail Queue and Mail Flow Tests

Mail Queue and Mail Flow Tests

Email sensors test mail flow and mail queues for Exchange, Office 365, SPAM providers, OWA and more. They test mail queues for performance and availability by sending small messages to the auto-responder at the exomail@exotester.com recipient.

The reply from the auto-responder is exoreturn@exotester.com. 

Message Transfer Agent, MTA or Mail Transfer Agent

Message Transfer Agent is the set of servers and software responsible for transmitting email messages from one computer to another. Within Exoprise CloudReady synthetics, we refer to mail flow statistics and performance as MTA.

Unblocking Mail Flow Tests

If you have a outbound SMTP filter that prevents sending mail to the auto-repsonder then you will need to unblock it.

If you have an inbound SPAM protection service that is blocking the auto-responder then you will need to unblock it and enable return mails from exoreturn@exotester.com.

Or you can choose to not test mail queues and Office 365 mail flow.


There are 3 primary metrics collected for mail flow and mail queue tests:

  • MTA Inbound
    The total time it takes to reply to an email from our auto-responders to the inbox. This metric measures inbound queue performance.
  • MTA Transport
    The time it takes for a reply to reach the inbound MTA servers. This metric measures inbound transport performance and is a subset of the MTA Inbound time as reported by processing servers.
  • MTA Outbound
    The time it takes to send an email to our Exoprise auto-responders. This metric measures outbound queue and transfer performance. MTA stands for message-transfer-agent and is responsible for the transmission of email between servers.

Best Practices

The email sensors are designed to not fill up a mailbox. Between a combination of Exchange Rules and automated cleanup as part of each sensor run, the email sensors strive to leave a mailbox intact.

Legal hold for mailboxes can prevent this deletion so it is not recommended to test mail queues against a mailbox with legal hold.

Related Articles