Bit of an odd one we had on Friday which I don't know if it's PRTG or cPanel/Exim at fault. Less a question, more an "if any other PRTG users get this it might be useful".
A POP3 Round Trip sensor we've had in place for a couple of years without issue went down with a last message of :
"Sending Mail: Access denied - Invalid HELO name (See RFC2821 4.1.1.1) "
Checked the server and other than our PRTG test emails there were no errors and email was flowing fine, confirmed Exim has "Require RFC-compliant HELO" enabled which it always has, and it's enabled on another identical cPanel server we have which wasn't having the issue in PRTG. Restarted Exim in case that had gone nuts but it made no difference. Confirmed PRTG was connecting from the usual IP, that reverse DNS was correct, that PRTG was annoucing itself the same as usual, and that the PRTG server was still on the cPanel server's allow list and hadn't been blocked by the firewall.
Grasping at straws I disabled the "Require RFC-compliant HELO" setting and the sensor came back up... then I enabled it again, and it's remained up ever since.
Edited copy of the entire PRTG debug log for that sensor from when it was down for reference.
--- 07/10/2022 22:17:06 - Start Work\\ 07/10/2022 22:17:06 - Initializing SMTP: \\ 07/10/2022 22:17:06 - Connection to SMTP Server: \\ Stat Connected.\\ Recv 07/10/2022 22:17:26: 220-mail.server.com ESMTP Exim 4.95 #2 Fri, 07 Oct 2022 22:17:23 +0100 <EOL>\\ 220-We do not author ... mail.<EOL>\\ Sent 07/10/2022 22:17:26: EHLO PRTG-SERVER<EOL>\\ Recv 07/10/2022 22:17:26: 250-mail.server.com Hello prtg-server.fqdn.com [<PRTG Server IP address>]<EOL>\\ 250-SIZE 52428800< ... HELP<EOL>\\ Sent 07/10/2022 22:17:26: STARTTLS<EOL>\\ Recv 07/10/2022 22:17:26: 220 TLS go ahead<EOL>\\ Sent 07/10/2022 22:17:26: EHLO PRTG-SERVER<EOL>\\ Recv 07/10/2022 22:17:26: 250-mail.server.com Hello prtg-server.fqdn.com [<PRTG Server IP address>]<EOL>\\ 250-SIZE 52428800< ... HELP<EOL>\\ 07/10/2022 22:17:26 - Sending Mail: \\ Sent 07/10/2022 22:17:26: RSET<EOL>\\ Recv 07/10/2022 22:17:26: 250 Reset OK<EOL>\\ Sent 07/10/2022 22:17:26: MAIL FROM:<[email protected]><EOL>\\ Recv 07/10/2022 22:17:26: 550 Access denied - Invalid HELO name (See RFC2821 4.1.1.1)<EOL>\\ ---
Last change on Oct 12, 2022 9:51:25 AM by
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