I have a Cobalt raq3. I can send email via POP, with the address cheatman.net(my domain)

for the smtp(to send email) I used the same address --cheatman.net

but it didn't work, is there a special one i have to use?
i tried smtp.cheatman.net, mail.cheatman.net


Anyone know of the correct address?

I'm guessing you don't have POP-Auth installed. By default, the RaQ does not allow you to relay mail. If you have this installed, then your ISP may be blocking all other SMTP servers.