Windows – How to add a domain to an IIS 6 SMTP server so that it will relay for that domain

If you're going to be sending email directly from the IIS SMTP server, then you don't need to configure any relay settings. The server sending outbound email from itself is not a relay. The tests you're running are exactly what you should expect when trying to send email through the server from another host (because relaying is not enabled). IIS SMTP is a fully functional SMTP server, and as such, requires no relay configuration unless other hosts will be sending email through it to external domains (domains not native to the IIS SMTP server). Again, if the IIS SMTP server will be sending email from itself to external domains, no relay configuration is required.

The SMTP service listens to port 25 on all unassigned IP addresses even if you specify a specific IP address for the default virtual server. You need to disable the Microsoft Internet Information Services (IIS) socket pooling feature (DisableSocketPooling). This property is not exposed in ADSI for SMTP.

http://support.microsoft.com/kb/281760

1. Install and run MetaEdit on the server.
2. Expand LM and SmtpSvc.
3. Right-click SmtpSvc, click New, and then click DWORD.
4. In the Id list, click DisableSocketPooling. The field to the right should now read 1029. If DisableSocketPooling is not in the list, click (Other), and then type 1029 in the box.
5. In the Data field, type 1.
6. Click to select the Inherit attribute.
7. Restart the Simple Mail Transport Protocol (SMTP) service.

Hope this helps.