rDNS and PTR records It is important that a rDNS record (also known as PTR record) is setup for your IP address.

An 'A' record resolves a HostName into an IP. For Example the 'A' record for mail.mailsite.com resolves to 216.34.131.10

A PTR records resolve IP addresses into hostnames. For example the PTR record for 216.34.131.10 resolves to mail.mailsite.com

Some mailservers require that the sending server have a PTR record. PTR records are managed within your DNS, and is outside the scope of MailSite Support. You should contact your ISP or DNS provider and ask them to create PTR records for your IP address.

AOL for example require that all sending mail servers (MTA's) have a PTR Record. You can use the following lookup tool on their site to verify the status of your IP:

http://postmaster.info.aol.com/tools/rdns.html