SMTP Checks

About SMTP Checks

SMTP stands for "Simple Mail Transfer Protocol," and refers to the service that sends and receives email around the world. SMTP services are critical for all email interaction.

It's important to verify that your SMTP servers are up and running but also verify that they're properly accepting email. We do this by monitoring not only the service but its ability to receive email for particular addresses. If your server uses SSL or TLS to secure mail transport, we can also monitor the functionality and validity of your certificates and send you an alert before they expire.

When to use SMTP Checks

NodePing's SMTP checks are an important part of an overall server monitoring strategy. The checks can not only verify that your server is accepting email properly but that user logins and your SSL/TLS certificates are also functioning properly. You can check to make sure that your SMTP server is not an open relay.

Using SMTP Checks

To set up an SMTP check,

  1. Select SMTP from the Check type drop down.
  2. Give it a friendly label to identify this check in lists and notifications.
  3. Enable Automated Diagnostics if you'd like detailed technical info about the failure that may help you troubleshoot a failure.
  4. Set how often you want the check to run on the Check Frequency field.
  5. Set the address or fully qualified name of the SMTP server and its port. SMTP servers commonly use port 25 for non-secure communications and port 465 for SSL or TLS.
  6. If your server supports SSL or TLS secure transport, select 'Use SSL/TLS on SSL Port' from the Secure dropdown. SSL/TLS is typically run on a different port than 25. If your server supports STARTTLS, you may alternately select it from that same dropdown.
  7. If you use SSL/TLS/STARTTLS, you can optionally select 'Verify certificate' in the Verify SSL Certificate drop down. The check will fail if the certificate does not pass verification. You may also optionally receive a notification when the certificate is approaching its expiration date by inputting the number of days before expiration you would like to notified in the Days field.
  8. The optional Verify Email drop down will verify that your SMTP server accepts or rejects mail sent to the email in the Email Address field.
  9. To verify that a particular user is able to log in to your SMTP server, provide the username and password in the appropriate fields. The following authentication mechanisms are supported: PLAIN, LOGIN, CRAM-MD5
  10. Set the Sensitivity. High is usually appropriate.
  11. Set the notifications for this check. More information about notifications.

Common usage:

  • To just check that a SMTP server is up and responding, just set the SMTP server name or ip address and port and leave the other fields blank.
  • To check that your SMTP server is not an open relay, select "Should accept mail for:" from the optional Verify Email drop down and enter the full email address in the Email Address field
  • To test that your server will accept email or a particular email address, select "Should accept mail for:" from the optional Verify Email drop down and enter the full email address in the Email Address field
  • To verify and receive an alert before your SSL certificate expires, select either 'Use SSL/TLS on SSL Port' or 'Use STARTTLS' from the Secure dropdown and specify the number of days in advance of the certificate expiration in the Days field.

Other considerations

Some SMTP servers have intentional connection delays to reduce spam. You may need to increase the default timeout to 15 seconds or higher to properly check these servers.

A check configured to test SSL/TLS against a non-SSL enabled port will time out waiting for an SSL handshake.

Thoroughly testing all aspects of your SMTP server may require more than one check, for example, one to test for open relay and one to test that it is properly accepting mail for an address.

If you have any questions, get in touch at, or use our Contact form.