There is one domain that bounces our emails on a regular basis. The domain is setup under google apps and we're sending from our exchange server. Our MX record, banners, etc appears to be fine and we're not having issues sending to any other domain. Sometimes it works, but usually it bounces.
There bounce message is:
firstname.lastname@example.org on 8/24/2015 9:25 AM
There was a SMTP communication problem with the recipient's email server. Please contact your system administrator.
<mail.pmcommunities.com #5.5.0 smtp;550-(mail.ourdomain.com) [nnn.nnn.nnn.nnn]:64923 is currently not permitted>
It seems it would be on their side. Even it is, I would like to help them fix it.