Why do I get "lost connection with somesubdomain.snwlhostedeu.com[173.240.221.30]..."

bitops

Hello,

i am trying to send E-Mails to a Domain which is using sonicwall HES as far as I can see.

But SMTP Connection fails with the following error:

"lost connection with somesubdomain.snwlhostedeu.com[173.240.221.30] while performing the HELO handshake)"

If I try to test with telnet I am getting "554 No SMTPd here...":

# telnet stl-nbg.de.snwlhostedeu.com 25
Trying 173.240.221.30...
Connected to stl-nbg.de.snwlhostedeu.com.
Escape character is '^]'.
220 ams0vm-hesra04.colo.sonicwall.com ESMTP snwlhostedeu.com
554 No SMTPd here   202106011956472107112;1544
Connection closed by foreign host.

I am not able to transfer E-Mails from this postfix E-Mail System to a Domain using HES.

Any Idea whats wrong here?

Is this some kind of feature of HES? Usually testing with telnet works on smtp servers and also some kind of reasonable error response like "blocked by RBL" etc. is given.

I appreciate any hint that leads me a step further.

best regards,

Sebastian

David W

@bitops this is your clue to the issue at hand.

554 No SMTPd here

This error means that the sending IP is listed in the IP Reputation database.

Thus the connection is blocked.

The most likely cause for this is not following best practices such as having a PTR record for the sending IP.

There can be a multitude of things that caused it to be listed.

You will want to open a case and ask to have the sending IP reviewed and will most likely then be greylisted and allowed to send.

bitops

Thank you for the quick response @David W

Ok, I think then this IP is somehow listed in the IP Reputation database, because PTR and other best practices are in place on this mailsystem and successfully sending mails to all other providers. Only snwlhostedeu.com does not accept mails at the moment.

I will open a case