I have a web server that is located behind the DMZ interface of our firewall. The website allows customers to send emails of collections lists. I have allowed the web server smtp access to the exchange server in our internal network. On the firewall audits I can see that the traffic is passing the firewall. The web server will send the email to internal email addresses, but when it tries to send to external email addresses, the exchange server returns a 550 unable to relay error message. I followed these directions from Microsoft (http://technet.microsoft.com/en-us/library/bb232021.aspx
), but the server still will not email external users. Any suggestions or assistance would be greatly appreciated.