Warning - Reverse DNS does not match SMTP Banner

Hello experts
I inhertied this network recently and all the sudden i'm getting emails not delivered to some domains " the connection dropped by the remote host"
When i use mxtoolbox.com to check my company SMTP diag, it shows the message below

Not an open relay.
 0 seconds - Good on Connection time
 0.250 seconds - Good on Transaction time
 OK - 65.xxx.xxx.98 resolves to
 Warning - Reverse DNS does not match SMTP Banner

Session Transcript:
HELO please-read-policy.mxtoolbox.com
250 server.domain.com Hello [64.xxx.xxx.133] [62 ms]
MAIL FROM: <supertool@mxtoolbox.com>
250 2.1.0 supertool@mxtoolbox.com....Sender OK [62 ms]
RCPT TO: <test@example.com>
550 5.7.1 Unable to relay for test@example.com [62 ms]
QUIT
221 2.0.0 server.domain.com Service closing transmission channel [62 ms]

I read the blog http://demazter.wordpress.com/2010/02/09/exchange-dns-configuration/

and i actually changed my fqdn to mail.domain.org and also created an A record that matched that and an mx record but i still got the same error and the emails dont go from any host in my network. an example of the domain i cant send to is  vnab.org
I have 2 domains domain.org and domain2.com  but all our emails are @domain.org however all the A hosts are configiured under domain2.com

Please advice me on what to do.
if necessary i can upload an image of the dns in my server if that is not dangerous to my network

Thanks