Can't send outside domain

Hopefully this is the last issue I come across, I have everything up and running an email server running Ubuntu 5.1 and postfix courier imap and can send and receive from the domain fine, I can receive from any other domain, I just cannot send to them. I have read a lot about port 25 being blocked by my provider, is that possible? When I try to send my mail client give this message:

Server replied: 554 <[email protected]>: Relay access denied

and I am tailing the mail.log and see this:

NOQUEUE: reject: RCPT:from unknown[my web server's ip address]

Is this enough information to determine some possible causes? thanks!!

Ok I also see this in the log:

ERROR:5.7.1:550 Mail Refused - res.rr.com - See http://security.rr.com/rrDynamic.htm (port 25) and when reading that site it basically says they block it, soooo...I'm out of luck??

 

You have to check "Server needs authentication." (or similar) in your email client.

 

The problem with your server is that your smtp daemon is trying to send email through an other server which does not allow relay. Check your configuration and remove any relay-smtp servers.