Question : DNS will not resolve one domain

I have a client running SBS 2003. Email to one person does not go through. I discovered that DNS can't resolve anything regarding that domain. I can ping www.domain.com and mail.domain.com from anywhere except that clients site. Other than failing to get to this one site, DNS works fine.

I cleared out the DNS cache
restarted DNS
ipconfig /flushdns.
Reset DNS server to defaults
All root hints are there.

If I put forwarders in DNS, the email goes out. I could leave it that way but more than anything, I am very curious what could cause this

Answer : DNS will not resolve one domain

Does your DNS server have forwarders configured?

If not configure forwarders to your ISP's DNS servers.

Open the DNS console, right click the DNS server, select properties and the forwarders TAB, enter your ISP's DNS servers into the appropriate field.

If no forwarders are configured you rely only on root hints, your ISP's DNS servers will be more reliable.