421 DNS:NR
 http://postmaster.info.aol.com/errors/421dnsnr.html


EXPLANATION:

Reverse DNS lookup for your IP address is failing. 

SOLUTION:

Reverse DNS is a way of associating an IP address with its domain name. The reverse DNS identifier is contained in the PTR portion of the IP Zone File. You may look at your reverse DNS using our reverse DNS search tool. 

If you are on a dynamic IP address, please call your ISP and request a static IP address with proper rDNS before attempting to send mail to AOL through that server. 

If you are on a static IP address, please call your ISP or DNS provider and ask them to establish a reverse DNS record for your IP address, reflecting your correct domain name.