how can I stop spam inpersonation of my domain?

Question

someone out there is using my domain inpersonating our company for spaming purposes, how can i find out who it is or repor them

Answer 1

The first thing I would check is your e-mail server to see if you have an open relay. Spammers scan the internet constantly, looking for exposed servers to route their e-mail.
Second, I would rename all my administrative accounts and change the passwords to lengthy, secure passwords that are hard to crack.
Third, I would run antispyware, followed by hijackthis to track any remote control programs that may have been installed without your consent.
Fourth, I would obtain some of the spam e-mail and check the headers to see where it's originating from.

Answer 2

What domain?

google, yahoo? Like which thingy is it? Report it to whatever server you using.