Reverse DNS

In addition to A records and MX records, reverse DNS records (or PTR records) are important as well. Many spam prevention solutions require the PTR record match the forward lookup record (which is usually an A record or a CNAME). The authoritative DNS server for the IP address is going to be your registrar. Therefore, the registrar should be able to create such a record for you.

Because you will need reverse DNS, it is highly unlikely that you will want to use a dynamic IP address as the public address of your mail server. If you do, few domains will accept your mail. Overall, this represents a few steps so far. First, obtain a domain name. Then build the correct records on the DNS service and finally contact the ISP to verify that you have a static IP address and that a PTR record has been created for the IP address that the server uses on the ISP’s DNS servers. This provides the best chance that the IP address being used will be allowed to relay outgoing mail as needed.