WebMail URL (A Record) - Add an A or CNAME record for mail.example.com that points to the IP address of the webmail interface. This will allow users of that domain to access the webmail by typing in http://mail.example.com or http://mail.example.com:9998 in their web browser (depending on whether you use the included web server or IIS).
Mail Pointer (MX Record) - Add an MX record for example.com that points to the IP address that you assigned when adding the domain to SmarterMail. This will allow other email servers to locate your mail server.
Reverse DNS Record - Add a reverse DNS record for IP addresses assigned on the server to provide extra assurance to other mail servers. Also, it is recommended that the primary IP address of the server also have a reverse DNS record. Note: Adding reverse DNS may also require a change at your isp.