Question : Exchange 2010 SMTP Relay

Need some direction. Recently installed a Exchange 2010 in a test environment.  Everything is working great. Everything but one majpr thing; clients that are configure for POP/SMTP can not send email. For example, I have people that do not use Outlook (require POP/SMTP). These people may reside on the public Internet.  I setup Outlook 2007 for POP/SMTP and put in the credentials.  I run the test procedure and I am able to send and receive the test message.  However after all is said and done, I can receive email but can't send (even though the test message worked fine).  Anyone have a guess or answer to why this is?

Answer : Exchange 2010 SMTP Relay

Thanks for the help. for some reason none of mu users had permission to send vie he conector. I used ADSI Edit and took care of that