I am going to report this to support and will post any response from them here (I have always had good luck with Chad's support responses).

Version: OptIn 02.06.00 (Opt In - Opt In Email is actually 02.06.10 but the others are .00)

The problem occurs when someone tries to subscribe. Everything appeared to be working fine when the site was set up and tested recently. No changes (AFAIK) were made to the SMTP server configuration and using the Configuration Test Opt In provides sends a correct test email.

When a user subscribes they see the following:

"Message Failed! Please contact support."

If I check the DNN Log Viewer I see the following error (InnerException):

The server rejected one or more recipient addresses. The server response was: 550 5.7.1 ... Relaying denied: You must check for new mail before sending mail.

I have logged into the mail server and ensured that the mailbox the SMTP is used as login to the SMTP server is cleared out (so new mail has been checked), etc.

It is one of my email accounts so I have verified I can send from Thunderbird using the same SMTP configuration and as I said above the SMTP Configuration Test from Optin works. DNN is using the same SMTP configuration to send out site emails (like new user sign ups) and it is working fine.

Any ideas where to start looking for a fix?

Thanks,

Scott