Host with "no rDNS" problem

webmasteryoda

Well-Known Member
Apr 3, 2013
97
7
8
Serbia
cPanel Access Level
Root Administrator
Hello

I have some issues with my email server. Its not sending emails to some hosts (mostly Microsoft servers).

Firstly, I must say that I configured my server few days ago. And its properly configured.

When I check mail-tester.com, my results are 8.8/10.
It says I am properly authenticated. SPF, DKIM, DMARC - all ok!

It also says that my rDNS is fine. But...

Spam Assassin thinks I can improve. Here is what Spam Assassin says:
-1.274 RDNS_NONE Delivered to internal network by a host with no rDNS
This may be a false-positive, please check the reverse DNS test below to confirm or not this issue

But, as I already said, my rDNS resolves to IP address from which I am sending email.
So, why are some servers seeing my rDNS as invalid.

I must say that I am using additional IP address, which is HELOing to my hostname (which is NOT a domain name of the sender).

Any clues?
 

cPanelMichael

Administrator
Staff member
Apr 11, 2011
47,913
2,203
363
Hello,

The following document is a good place to start if you want to ensure your server is following the best practices for successful delivery to remote mail servers:

How to Keep your Email out of the Spam Folder - cPanel Knowledge Base - cPanel Documentation

I must say that I am using additional IP address, which is HELOing to my hostname (which is NOT a domain name of the sender).
If you have configured Exim to use a different IP address, the PTR record of that IP address should use the hostname of your server. Do you receive a specific bounce message from the servers that are rejecting your messages?

Thank you.
 

webmasteryoda

Well-Known Member
Apr 3, 2013
97
7
8
Serbia
cPanel Access Level
Root Administrator
Sure. Here is delivery report from one of these messages:
SMTP error from remote mail server after RCPT TO:<[email protected]>: 451 bad reverse dns

But it is not a bad reverse dns. Here is my servers setup:

111.111.111.111 (main servers IP) - hostname.server.com
222.222.222.222 (dedicated IP for a sending domain) - sendersdomain.com

rDNS for both IPs = hostname.server.com

/etc/mailhelo:
sendersdomain.com: hostname.server.com
*: hostname.server.com

/etc/mailips
sendersdomain.com: 222.222.222.222
*: 111.111.111.111

Is this preferable configuration?
 

cPanelMichael

Administrator
Staff member
Apr 11, 2011
47,913
2,203
363
Hello,

Here's a quote from our documentation regarding the manual changes to those files:

To use a custom Exim configuration, enable the following options in the Basic Editor section of WHM's Exim Configuration Manager interface (Home >> Service Configuration >> Exim Configuration Manager):
  • Reference /etc/mailhelo for outgoing SMTP HELO
  • Reference /etc/mailips for outgoing SMTP connections
As far as your configuration:

/etc/mailhelo:
sendersdomain.com: hostname.server.com
*: hostname.server.com

/etc/mailips
sendersdomain.com: 222.222.222.222
*: 111.111.111.111
In the /etc/mailhelo file, you can leave "*: hostname.server.com" as the sole entry in this file. This information is documented at:

How to Configure the Exim Outgoing IP Address - cPanel Knowledge Base - cPanel Documentation

How long ago was the RDNS entry updated? Could it be an issue where the DNS change has yet to propagate?

Thank you.
 

webmasteryoda

Well-Known Member
Apr 3, 2013
97
7
8
Serbia
cPanel Access Level
Root Administrator
Yes, I followed that article when configuring mail server.

RDNS was changed 2 days ago. So, it should be fine?

Is it possible to use 2 different HELOs on the same server?
(both IP addresses to have different reverse DNS and configured on the same server?)
 

webmasteryoda

Well-Known Member
Apr 3, 2013
97
7
8
Serbia
cPanel Access Level
Root Administrator
Hello

Its been awhile since I posted this. I was researching the problem, and I`ve read all of the articles, but the problem stays.

I didnt solved it.

But here`s an interesting detail.

When I do:
dig +short -x @localhost xxx.xx.xx.xxx (my main servers IP)

I get nothing!
My own server cant find RDNS ???

How can it be?
 

cPanelMichael

Administrator
Staff member
Apr 11, 2011
47,913
2,203
363
Hello,

Feel free to open a support ticket using the link in my signature if you'd like us to take a closer look.

Thank you.