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SMTP/pop3 round trip setup Error PE039



We are setting up a SMTP/POP3 sensor and we are getting a PE039 error. We understand that it means that the connection dropped. https://kb.paessler.com/en/topic/32813-what-does-error-code-pexxx-mean#reply-217142

We are trying to find out were it dropped? We check the gmail account and the internal email account. We see that both are getting the emails.

gmail-smtp-settings pe039 roundtrip smtp-gmail-com

Created on Sep 26, 2018 10:00:40 PM

3 Replies



Hello there,

For one the sensor sends an email out, it uses the parent device as SMTP to do so, that's one possibility for the connection drop. The other one is when checking the other account for the email. To be sure where this drop is being noticed, you need to trace this at connection level, for example by running a Wireshark capture and then check what happened there at the time the sensors reports this error again.

Kind regards,


Created on Sep 27, 2018 11:45:19 AM by  Erhard Mikulik [Paessler Support]



Thanks for the help. we had the wrong port on the pop3 settings. Getting new error, Connecting to POP3 Server: Socket Error # 10060 Connection timed out. I want to verify that I have the IP- Address/DMS name entry correct.

IP- Address/DNS name : pop.gmail.com port : 995 connection Interval : 30 Maximum trip time : 300 POP3 Authentication Type : Username and password

POP3 Specific : Use Transport-Level Security if available using StartTLS (default)

I have verified the username and password.

We are getting emails in the gmail account. So SMTP is working. Not sure if PRTG goes to gmail and attempts to logon and send a reply.

Created on Sep 27, 2018 7:45:31 PM



This whole email roundtrip thing consists of three steps, see also here.

You add the sensor to a device that is an SMTP server, this one is being used to send the email out, I guess in your case it sends it then to a gmail account. From there usually you should have a rule in place that forwards this email to a different mailbox where the sensor tries to fetch this email then (step 2 in the sensor's settings). When the email arrives at gmail, then the sending part is covered and the error is related to the "pulling" part when trying to check the other mailbox if the mail has arrived.

Created on Sep 28, 2018 12:52:55 PM by  Erhard Mikulik [Paessler Support]

Last change on Feb 22, 2023 11:02:24 AM by  Brandy Greger [Paessler Support]

Disclaimer: The information in the Paessler Knowledge Base comes without warranty of any kind. Use at your own risk. Before applying any instructions please exercise proper system administrator housekeeping. You must make sure that a proper backup of all your data is available.