Hi, I read at http://msexchangeteam.com/archive/2006/12/28/432013.aspx that : Allow all computers which successfully authenticate to relay, regardless of the list above Like its predecessor, Exchange 2007 is configured to accept and relay email from hosts that authenticate by default. Both the "Default" and "Client" receive connectors are configured this way out of the box. Authenticating is the simplest method to submit messages, and preferred in many cases. The Permissions Group that allows authenticated users to submit and relay is the "ExchangeUsers" group. The permissions that are granted with this permissions group are: NT AUTHORITY\Authenticated Users {ms-Exch-SMTP-Submit} NT AUTHORITY\Authenticated Users {ms-Exch-Accept-Headers-Routing} NT AUTHORITY\Authenticated Users {ms-Exch-Bypass-Anti-Spam} NT AUTHORITY\Authenticated Users {ms-Exch-SMTP-Accept-Any-Recipient} The specific ACL that controls relay is the ms-Exch-SMTP-Accept-Any-Recipient. I have a software that send email with my SMTP exchange 2007 server. I enter the login and password of my user to authenticate the user. When I sent an internal email, I have no error but when I sent the mail to an external email, I received the error: 5.7.1 Unable to relay on my software. I tried the same software connected to my exchange 2003 and an 2003's user, the email is sent. Any idea why my echange 2007 do not relay when an user is authenticated? Do I need to create a new connector? The default connector needs to allow relay when an user is authenticated? Thanks