If you do not run your own DNS server, THIS is an example of how you would need to submit your rDNS information :
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Subnet 76.73.90
13 86400 IN PTR server1.host1.com. ;
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The Lowest TTL we can have it is 3600, so keep that in mind.
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If you have your own rDNS servers, replace IN PTR with IN NS, and that will point DNS to go back to your server for DNS entries. When you want us to apply your changes, please email us : support@madgenius.com, stating you want rDNS setup.