<%NUMBERING1%>.<%NUMBERING2%>.<%NUMBERING3%> PRTG Manual: Monitoring Email Round Trip

Email Round Trip sensors ensure the end-to-end delivery of emails and let you monitor the availability and the performance of a complete email delivery process. There are two sensors for this task:

Both initially deliver an email to a mail server using the Simple Mail Transfer Protocol (SMTP). Afterward, the receiving mailbox is scanned using Post Office Protocol version 3 (POP3) or Internet Message Access Protocol (IMAP) until the email arrives. The test email contains a unique code in the topic that is used to identify the email, such as PRTG Roundtrip Mail: {6D136420-5A3E-46CF-871A-1DAF0C4F3D5D}

When PRTG successfully receives an email in this email round trip cycle, it marks the respective message for deletion on the mail server. Usually, a mail server then deletes this email. For best performance, we recommend that you use dedicated email accounts for email round trip sensors.

Monitoring an Email Round Trip

Monitoring an Email Round Trip

In the scenario shown above, there are three steps in the round trip:

  • Step 1
    PRTG delivers an email via SMTP to a mail server (like an email client).
  • Step 2
    The SMTP server delivers the email to a POP3/IMAP server (which can be located at a remote site, in your local LAN, or on the same server as well).
  • Step 3
    Every few seconds, PRTG connects to the POP3/IMAP server until the test email arrives.

Recommended Configuration

Here is a simple concept to check the delivery of email from and to your organization:

  1. Create a dedicated email account for this test in your mail system.
  2. Set up an external email account (for example, on a hosted mail server or free mail service) and configure it to send all emails back to this dedicated email account in your organization (that you created in step 1).
  3. Set up a Round Trip sensor to send an email to the external email account (that you created in step 2) using your network's mail server and then check for the email account on your mail system (that you created in step 1) for the arrival of the email.

With this technique, you are testing multiple aspects of your email server setup. As long as the sensor shows the Up status, this means:

  • Your email server accepts emails via SMTP.
  • Emails are being sent to the outside world. So the internet connection and MX lookups work.
  • Emails from an external mail server can be delivered into your mail system. So the MX records for your domain are correct and the mail server is reachable from the outside world. Also, your email filtering is working.
  • Emails can be retrieved using POP3 (or IMAP).

Use dedicated email accounts with this sensor. If you use more sensors of this type, make sure that each sensor uses its own email accounts.


These two sensors ensure the delivery of email from and to your mail servers. Compared to the standard SMTP, POP3, and IMAP sensors that only check the availability of these services, the two round trip sensors actually monitor the complete transaction from accepting the email on the first email server to the delivery of the email to the final POP3/IMAP server.