504 Access to this service has been denied by the mail administrator

I have an e-marketing application that was developed in ColdFusion 7 and uses an Access database.

I have recently migrated the database to SQL Server Express 2012 and ColdFusion 10. However, it has now stopped working, although the same code works on CF7.

The app is accessed via a browser based interface and allows the user to schedule the automated sending of emails and also specify what the delay should be between sending each. For instance, I may send 100 emails and set the delay to 4 seconds between each.

When I look in the logs I see: javax.mail.AuthenticationFailedException: 504 Access to this service has been denied by the mail administrator

Does anyone know what I need to do enable the service?