SMTP Reverse DNS Issue

[SwanseaK]

Hello,

I run Plesk 12 on Centos 5.5.

When I check on MXToolbox, it shows my servers has a SMTP Reverse DNS Issue.

Here are details:

1. SMTP Banner check on MXToolbox output is:

SMTP Banner Mismatch
​

2. Result of telnet mail.example.com 25 command output is:

Trying **.**.**.***...
Connected to mail.example.com.
Escape character is '^]'.
220 example.com ESMTP

**(This outputs as 220 example.com ESMTP rather than 220 mail.example.com ESMTP)​

3. Result of host smtp.example.com command output for my server is:

smtp.example.com has address **.**.**.***​

But host **.**.**.*** command output for my server is:

**.**.**.***.in-addr.arpa domain name pointer example.com.​

It does not resolve to smtp.example.com but to example.com for my server. To me, it seems to be correct and logical but below MXToolbox description states the correct SMTP reverse DNS syntax which I copied from official MXToolbox​

Example of a correctly matching pair of records:
(A) lookup for smtp.mxtoolbox.com resolves to 208.123.79.38
(PTR) lookup for 208.123.79.38 reverses to smtp.mxtoolbox.com​

4. I have only 1 website and domain on my server. The registered domain on Plesk hostname is example.com. I am not sure if I should change Plesk hostname to something like myserver.example.com

I am not sure my about this issue. PTR lookup resolves correctly to my server, example.com but MXToolbox expects it to resolve to smtp.examle.com

Do you have any recommendation about this problem and how can I fix it please?

 

[UFHH01]

Hi SwanseaK,

Do you have any recommendation about this problem and how can I fix it please?

Well, there is no problem at all, if SPF - entries and/or DKIM - entries point to the correct IP and A - records.

Please have valid and existent A - record on your nameserver(s) for mail.example.com .
Please have a look at for example:

http://talk.plesk.com/threads/emails-from-php-are-waiting-but-not-send.335182/#post-789000
http://talk.plesk.com/threads/webmail-aplication.334481/#post-786285 ( and following posts in this thread )​

... to see what else is relevant for a correct mail - server configuration.
Please don't only use one solution, to validate your configuration. Here are some more usefull sites:

http://www.mail-tester.com/
http://dkimcore.org/tools/
https://dmarcian.com/dmarc-inspector/
https://www.ssllabs.com/ssltest/index.html​

 

[SwanseaK]

Thank you very much for your help @UFHH01.

I have validated I have correct SPF.

I have A record for mai.example.com.

Mail-tester.com shows 10/10. But it warns me that I do not have DMARC although I have DMARC DNS entry set.
Dmarcian.com also sees my DMARC as set correctly.
MXToolbox shows as my server has SMTP rDNS mismatch.

I seem to have correct DNS settings. But I do not understand why MXToolbox and Mail-tester.com warns me about. I thought whole situation might be about MXToolbox's smtp.example.com reverse dns issue, but as you said it should not be problem.

Can I disregard the Mail-tester.com's DMARC warning, too?

 

[UFHH01]

Hi SwanseaK,

Can I disregard the Mail-tester.com's DMARC warning, too?

hm... I can't give you a satisfying reply, if I don't know the actual test - results and don't know the FQDN domain name. There is a reason, why Mail-tester.com warns you. If you would like a decent answer to your question, you have to provide the domain - name, so I am able to investigate the issue.

 

[danallen1]

When I check on MXToolbox, it shows my servers has a SMTP Reverse DNS Issue.

mxtoolbox made that report falsely on a domain I support.

I verified with my vps provider, digital ocean, that my setup was valid. Then I called mxtoolbox. A guy named Jeremy answered. He said the mxtoolbox report was wroing. He provided me the following email:

 

[SwanseaK]

mxtoolbox made that report falsely on a domain I support.

I verified with my vps provider, digital ocean, that my setup was valid. Then I called mxtoolbox. A guy named Jeremy answered. He said the mxtoolbox report was wroing. He provided me the following email:

View attachment 10356

Thanks @danallen1 for your help. Much Appreciated.

 

[danallen1]

i was pretty relieved when I got that email, because I was getting static from a guy who benefited from being able to say the mail was not getting through due to invalid credentials on the sending server. This removed his ability to do that. Feels good to be able to pass it on, too.