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PRTG - Debugging SMTP failures for notification email



I just installed PRTG on Windows Server 2008r2, and I'm unable to get email notifications to work.

My mail is hosted remotely, not on this server. I have set up Notification Delivery as " Use one SMTP relay server (recommended in LANs/NATs) " SMTP server is mail.mydomain.com, port 587, Use standard SMTP authentication , Use SSL/TLS if the server supports it (default) , SSLv2 or SSLv3 (default) .

After testing the send, The log shows "Error sending "Email": SMTP relay server ("mail.mydomain.com") connection failed"

I enabled logging in the registry and found the following log for the PRTG test email (IP and domains obfuscated)

Stat Disconnected. Stat Connected. Recv 10/23/2021 1:16:11 PM: 220-box5623.bluehost.com ESMTP Exim 4.94.2 #2 Sat, 23 Oct 2021 12:15:33 -0600 <EOL> 220-We do not authorize the use of this system to transport unsolicited, <EOL> 220 and/or bulk e-mail.<EOL> Sent 10/23/2021 1:16:11 PM: EHLO SUN<EOL> Recv 10/23/2021 1:16:11 PM: 250-box5623.bluehost.com Hello SUN [136.***.***.141]<EOL> 250-SIZE 52428800<EOL> 250-8BITMIME<EOL> 250-PIPELINING<EOL> 250-PIPE_CONNECT<EOL> 250-AUTH PLAIN LOGIN<EOL> 250-STARTTLS<EOL> 250 HELP<EOL> Sent 10/23/2021 1:16:11 PM: STARTTLS<EOL> Recv 10/23/2021 1:16:11 PM: 220 TLS go ahead<EOL> TLS handshake failed Recv 10/23/2021 1:16:11 PM: urity failure<EOL> Sent 10/23/2021 1:16:11 PM: QUIT<EOL> Recv 10/23/2021 1:16:11 PM: 554 Security failure<EOL> Stat Disconnected. Error sending "Email": SMTP relay server ("mail.mydomain.com") connection failed

From my server, I can use cmail.exe and successfully send email through my SMTP relay. Here is the log from that:

C:\>cmail.exe -host:[email protected]:*********@mail.mydomain.com:587 -d -to:[email protected] -from:[email protected] "-subject:cmail-test2 ody:cmail-test2.cmd testing" Connected rx: "220-box5623.bluehost.com ESMTP Exim 4.94.2 #2 Sat, 23 Oct 2021 12:25:06 -0600" rx: "220-We do not authorize the use of this system to transport unsolicited," rx: "220 and/or bulk e-mail." tx: "ehlo []" rx: "250-box5623.bluehost.com Hello [] [136.***.***.141]" rx: "250-SIZE 52428800" rx: "250-8BITMIME" rx: "250-PIPELINING" rx: "250-PIPE_CONNECT" rx: "250-AUTH PLAIN LOGIN" rx: "250-STARTTLS" rx: "250 HELP" tx: "auth plain" rx: "334" tx: "AFN5c01lc2dAc3ludGhpZnkuY29tADEzNTc5X0luZm8=" rx: "235 Authentication succeeded" tx: "mail from: <[email protected]>" rx: "250 OK" tx: "rcpt to: <[email protected]>" rx: "250 Accepted" tx: "data" rx: "354 Enter message, ending with "." on a line by itself" tx: "X-Mailer: Inveigle.net CMail 0.7.9b (https://www.inveigle.net)" tx: "Date: Sat, 23 Oct 2021 18:25:44 GMT" tx: "From: "[email protected]" <[email protected]>" tx: "To: "[email protected]" <[email protected]>" tx: "Subject: cmail-test2.cmd testing" tx: "Message-ID: <lPU4hkpSXR4BMoF8Q$200974a48$6664@sun>" tx: "" tx: "cmail-test2.cmd testing" tx: "." rx: "250 OK id=1meLha-000a5L-SN" tx: "quit" rx: "221 box5623.bluehost.com closing connection"

It appears that PRTG is not sending the "auth plain" authentication handshake, and instead uses STARTTLS. Which options in PRTG will result in the process that is accepted by my host's SMTP server?

email notification prtg smtp

Created on Oct 23, 2021 7:02:39 PM

1 Reply



In case anyone else runs into this, after trying all the options one by one, it turns out that TLS 1.2 is the correct setting.

Better diagnostic information from the Test SNMP function would be helpful in future versions of PRTG.

Created on Oct 27, 2021 12:54:41 PM

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