I cant Seend Mails out from my machine

[hdbs007]

Hello all
I a made a new install of my ispcp and now I cant seend mails out , I receive mails from other people but when I seend it back nothings goes to them.I have my router port http, ftp, pop2 pop3 and smtp open.
I dont think it is a port problem,
I try to seend mails to other emails accouts that I have on my machine and it works, so I just cant seend out of it emails that dont belongs to the domains I'm hosting there.
Any tips?