DNS_FAILED?

At fist you should check if the recipient's address is valid:
- Browse to http://dnsstuff.com
- Perform a PING with the recipient's domain name there.
- If PING cannot resolve the domain name to its IP address, 
  then this name is invalid.

If it IS valid, then it might be a problem with your local 
and/or your ISP's DNS server.

See http://www.dnsstuff.com/ for some useful online services.
Search your system help pages for nslookup, ipconfig 
(=ifconfig on Linux).

These tools will help you to diagnose your DNS.
