Why SMTP Reverse DNS Mismatch Reverse DNS does not match SMTP Banner?

I have set rDNS to mail.simplyislam.biz for IP 178.32.48.104 with my hosting server and also in DNS control panel.

However, I am still failing this test

Result: SMTP Reverse DNS Mismatch Warning - Reverse DNS does not match SMTP Banner. See attached

But as far as I can see my rDNS for the IP address are both the same: mail.simplyislam.biz

I am at a loss as to how to fix the issue please ?

Solution 1:

Reverse DNS does not match SMTP Banner

The SMTP Banner is the response of your mail server for the ehlo query. Currently your mail server is closing the connection. That is the reason for the mismatch between rDNS and SMTP banner. Reverse DNS itself is set up correctly, though.

# telnet mail.simplyislam.biz 25
Trying 178.32.48.104...
Connected to mail.simplyislam.biz.
Escape character is '^]'.
ehlo example.com
Connection closed by foreign host.

Having looked a little deeper, your DNS and mail server configuration seems a little messy:

> set type=mx
> simplyislam.biz
…
simplyislam.biz MX preference = 0, mail exchanger = mail.simplyislam.com
simplyislam.biz MX preference = 90, mail exchanger = mail.simplyislam.biz

> mail.simplyislam.biz
…
simplyislam.biz MX preference = 0, mail exchanger = mail.simplyislam.com
simplyislam.biz MX preference = 90, mail exchanger = mail.simplyislam.biz

> simplyislam.com
…
simplyislam.com MX preference = 5, mail exchanger = simplyislam.biz
simplyislam.com MX preference = 30, mail exchanger = mail.simplyislam.com

Your domain (the part behind the "@" in an email address) needs a MX record pointing to your mail server:
simplyislam.biz. 3600 IN MX 10 mail.simplyislam.biz.

Then you need an PTR record pointing your IP address to your mail server, but that does already exist:
104.48.32.178.in-addr.arpa. 3600 IN PTR mail.simplyislam.biz.

Your mail server address does not need an MX record, unless you are expecting emails sent to "@mail.simplyislam.biz".

Of course you need to do the same things for your primary mail server "mail.simplyislam.com".