rDNS errors on secondary shared IP

I have been receiving ongoing complaints about client's email being rejected, and it is because the shared IP they are on doesn't have a proper rDNS record. I have been filing tickets with them (IBM) for 2 months and their response has been the same, the rDNS record is correct. It finally dawned on them, and I guess me, that the complaints are with the secondary shared IP, not the primary shared IP.

Both IP addresses have errors regarding:
SMTP Banner Check Reverse DNS does not match SMTP Banner
SMTP TLS Warning - Does not support TLS.

However, the secondary IP gets this error when checked in MXLookup:

SMTP Reverse DNS Mismatch Reverse DNS does not contain the hostname

Since cPanel supports multiple shared IP address, it would see there would be a way to give the secondary IP address a proper rDNS record.

This issue has caused me a lot of problems for months now and I would like a definitive answer "from the horse's mouth" before I start changing 50 domain IP address, something I don't care to do.

Running CENTOS 6.9 standard [server6] v68.0.20

Thanks!

 

Hello Michael. I was told by Softlayer to change the RDNS settings through their portal, not something done on the server. Their portal shows the RDNS has been set for the offending IP:

75.126.215.47

Status
N/A

Description
N/A

Hostname server6.linkuphosting.net

Compare that to the primary IP:

173.192.126.34

Status
In Use

Description
server6.linkuphosting.net

Hostname server6.linkuphosting.net

You can see on the one that works, it shows a Status of In use, and the description has the host name in it, the offending one doesn't.

If I use the "check all IPs in the subnet, it says:

75.126.215.47
In Use
Routed to 173.192.126.34

Not sure why this part of the portal says "in use", when the other section doesn't.

I don't know what role their management software has vs. what is controlled by the server itself. I don't know why these changes are done in their portal, not through the server itself.

My novice opinion is that they only let one IP be primary, and they only let one IP have a functioning RDNS.

Thanks,
Lew

 

Hello!

Per the conversation in the ticket, it isn't a matter of what settings are in cPanel, the RDNS info is provided by my hosts portal. So far, it seems they are only able to set up a proper RDNS on the primary IP, and not the secondary IP. That means half of my users can't send mail to a variety of places like Craigslist, Earthlink, etc...

Thanks Softlayer/IBM