The Mail Transfer (SMTP) monitor works by connecting to a mail transfer server and optionally checking for the existence of a specified mail account.
When you select "Mail Transfer (SMTP)" from the Service Type pop-up menu, the following sheet will appear:
Note: Mail Transfer (SMTP) services are completely separate from Mail Delivery (POP3) services, even if in some cases they can be run by the same program. For complete checking of your mail system, you should use both types of monitors on your mail server.
The optional "Verify e-mail address after connecting" field can be filled in with the name of a valid email account on the server.
Note that some SMTP servers do not allow the use of this command without being logged in. Since the monitor does not attempt to log in, you should leave this field unchecked on these servers.
The Mail Transfer (SMTP) monitor first initiates a connection to the service and waits for a "220" response. It then sends a "HELO" command to the service and waits for a "250" response to indicate that the service is ready to communicate with the monitor.)
If the "Verify e-mail address" box is checked, the monitor then sends a "VRFY" command, and waits for a "252" response to indicate that the specified user account was found.
If the monitor receives the "250" response (if the "Verify e-mail address" box is unchecked) or the "252" response (if it is checked), the test is successful.
If the monitor receives an error response (usually a "4xx" or "5xx" response code) at any step of the check, the test will fail with an error.
If the monitor does not receive the expected response at any step of the check, it will continue to wait for the desired response before continuing to the next step. If the desired response is never received, the test will fail with a timeout error.