Error during test of SMTP configuration

I'm attempting to configure e-Newsletter to use a SMTP relay service, but I keep getting an error message when I go to test the settings:

Failed to send test email! - Please check your outgoing email settings and server config to see if selected ports are open. Error details: The following From address failed: : Called Mail() without being connected

The SMTP relay service requires the MD5 Challenge and Response to be set for the password, but I don't see this setting in eNewsletter and my first guess is that this is the source of the error.

Any suggestions?