What does "Reverse DNS does not match your SMTP Banner" mean?

The reverse IP address name (PTR) is not contained in the server HELO or EHLO banner. In the example below, the string "someotherdomain.com" is not found anywhere in the server banner, which is reporting "example.com". This is only a warning, and in some cases you might not have control over it.

Example of incorrectly matching pair:

220 mx.example.com StrongMail SMTP Service at Wed, 09 Sep 2009 17:00:01 -0700

Not an Open Relay.
0 seconds – Good on Connection time
0.156 seconds – Good on Transaction time
OK – 1.2.3.4 resolves to mail.someotherdomain.com

Best practice would have 1.2.3.4 resolve to mx.example.com

Some mail servers look for this and use it to mark messages you send as questionable. Most mail systems will not reject your messages outright, but this might affect your spam score, increasing the likelihood that your messages will be marked as spam. We recommend that you contact your ISP and ask them to set up a reverse record (PTR) that matches the hostname of your mail server.