Hello Cory,
Thank you for reaching out to the SmarterTools community. This is most likely a configuration issue. I would recommend checking your bindings and making sure that the loopback address is able to access the POP port. You can find this in Settings->Bindings->Ports. Please let me know if this helps.
Kind Regards,
Zach Sylvester
Software Developer
SmarterTools Inc.
www.smartertools.com