Resolved SMTP - Reverse DNS is not a valid Hostname

[yemindo]

Server operating system version

Debian 9.13

Plesk version and microupdate number

Plesk Obsidian 18.0.44 Update #3

Hello,

I run a server that hosts multiple customers and domains.
Unfortunately, I can't get this warning out.





Do I still need to add a DNS entry? Glad for any help

 

[Kaspar]

Looks like your reverse DNS doesn't match the SMTP sender, which usually is the host name of your server. The IP for mail.sitecolor.de is 146.0.42.97, which in turn resolves to the reverse DNS of yemindo.de. Thats a miss match.

 

[yemindo]

Looks like your reverse DNS doesn't match the SMTP sender, which usually is the host name of your server. The IP for mail.sitecolor.de is 146.0.42.97, which in turn resolves to the reverse DNS of yemindo.de. Thats a miss match.

Hello Kasper,
thank you very much for the problem description. But I do not understand how to solve the problem.

A more detailed explanation.
The server has 2 IP addresses with one rDNS entry:
146.0.42.97 - yemindo.com
213.202.211.180 - yemindo.de

In the Plesk server setting the hostname is yemindo.de

There are several websites on this server,
like for example sitecolor.de, example1.de, example2.de

I have tried with more entries but it seems to bring nothing:
NS - mail.sitecolor.de. => ns1.yemindo.de
NS - mail.sitecolor.de. => ns2.yemindo.de

Do I need to change any of the entries or do I need to add something else?

 

[Kaspar]

Unfortunately, I can't get this warning out.

View attachment 21780

This is from the result from a mxtoolbox test right? Are you also having trouble with sending email or are you only concerned with the warning from the mxtoolbox test? From what I can gather this warning can often be ignored as it does necessarily indicate a problem.

You're DNS records seem fine. However the issue seems to be that mxtoolbox expects the host name of your server to be a (valid) sub domain. Like server.yemindo.de instead of just yemindo.de. Which it won't see as a valid host name, hence the warning. I am not sure if that's a RFC requirement. But as far as I know it should not cause any problems.

If you don't have any trouble with sending email you could leave it as is. Otherwise you'll have to change the host name of your server (and update the rDNS accordingly).

 

[mow]

You're DNS records seem fine. However the issue seems to be that mxtoolbox expects the host name of your server to be a (valid) sub domain. Like server.yemindo.de instead of just yemindo.de. Which it won't see as a valid host name, hence the warning. I am not sure if that's a RFC requirement. But as far as I know it should not cause any problems.

I have run into the same problem and checked the RFCs, but found nothing that would require a 3rd level. See also Definition of Fully qualified domain name. So I'm pretty sure this is mxtoolbox overreacting.

 

[yemindo]

Hello kasper,
thank you very much for your help. The message had no effect. The mails all go through without any problems.

However, I have been able to solve the problem.
As you said I changed the rdns to rdns.yemindo.de.

Thanks a lot