new SBS2003 install, SMTP fails on all emails


I've set up a new SBS2003 and for some reason the SMTP fails.

No users can email outside of the server. sometimes you get errors:

There was a SMTP communication problem with the recipient's email server.  Please contact your system administrator.
            < #5.5.0 smtp;550 #5.1.0 Address rejected.>

sometimes nothing....

any ideas where to start?
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spandexandyConnect With a Mentor Commented:
You can start by opening Exchange System Manager and checking the "Smallbusiness SMTP Connector" properties of your routing group. Your outgoing SMTP mail will either be directed to go through your ISP (by using a smarthost) or your server will try on it's own to connect to send the mail directly to the recipients. I use the smart host (using SMTP details provided by my ISP) in my network.

Is that sending email or receiving email?
It isn't an Exchange error, so the remote server is rejecting the message. Is it always the same error? If so are you routing outbound email through a smart host? It could be the smart host is rejecting the message.

You did open port 25 on your router/firewall and point to the server ip? Correct?
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