* mail server not work on NT through cable modem

[ts1]

I had tried many mail server, on my Windows NT or Windows 2000 server, my 
server connect through cable modem which assigned by DHCP server an IP address, 

my computer installed windows 2000, and I had tried Rockliffe Mailsite, Imail, 
etc , mail server.

my computer is connect through cable modem to internet, ISP use DHCP server to 
assign an IP address on my computer

but got same problem, when I use my own configed mail server to send mail, all 
message will go to holding, and system event viewer show, no response from any 
DNS server when searching for domain..."

but I got no problem to send and receive email which domain configed under my 
own DNS(on my NT server).

any help will be much appreciated.

thanks

ts