Message bounces due to a reverse DNS lookup are caused by the intended recipient's mail server. Some mail servers may employ a reverse DNS lookup as a means to detect possible spam. This could pose a problem for anyone using hosted spam filtering or email routing services, since the public MX records will be pointing to that service rather than the mail server itself. Most reverse DNS lookups simply look to see if the IP of the sending server has a PTR record which assigns a name to the IP. All of Webservio's filtering, routing, mail bagging, and email continuity servers have PTR records, so reverse DNS lookups should not cause any delivery problems.
Occasionally, a receiving mail server is configured to compare part of an email to the MX records for the sending domain. However, this is not a recommended configuration because MX records are used to designate a location for inbound mail delivery and do not mandate that the server which receives inbound mail is the same server which sends outbound mail for the same domain.
If a receiving mail server only accepts inbound mail from servers that have the domain name listed MX records, they will not be able to accept mail from a significant number of senders because of the increasing prominence of third-party mail processing services.
