My problem is similar to what 'ike' posted a month ago, but different enough that I thought a new thread was in order.

When a user registers for my portal, they get the following error:

There was an error sending confirmation emails - The message was not delivered to the following address(es) - . However, your user account was created successfully.

 I've checked that I have a host e-mail address set, and that the SMTP settings are configured; when I click 'test' I get my test message, and there is no error.  I do receive notification e-mails when I set up child portals.  So why does this e-mail operation fail?  What am I missing?

Sebastian,
We are encountering the failed email message for the Forgot Password form:
"Password could not be sent at this moment. Please try again later or contact the site administrator."

and the Registeration form:
"There was an error sending confirmation emails - The message was not delivered to the following address(es) . However, your user account was created successfully."

Is the "relaying" you mentioned a DNN setting or an ISP control panel configuration? Currently, the designated admin user (Admin > Site Swettings > Advanced Settings > Other Settings) has an email address that matches the primary host domain for the SNN site and the SMTP authentication credentials (Host > Host Settings > Advanced Settings > SMTP Server Settings) specify the username/password of the email box for that admin user. The Forgot Password form works for the admin (since the email recipient matches the domain), but others trying to retreave their passwords (with emails from different domains) get the unhelpful message.

Any guidance would be appreciated.
King

In Host Settings -> Advanced Settings -> SMTP Server Settings Change the Authentication from Anonymous to Basic and in the Username and Password boxes put the details for your smtp account. If you use anonymous it usually works for send email to yourself, but not much more.