Go Daddy has sometimes been a problem. They tend to interfere with email more than most other hosting providers.
I will share this post with our development team and see if they have any ideas as to what might be happening. In the meantime it would be helpful if you could please include the following information in the forum. Please do not include your domain name since this is a public forum.
http://sendpress.com/support/knowledgebase/what-information-should-i-provide-in-a-support-ticket/
Also, could you please let me know if you have tried sending through Gmail? You could also try sending a test to me. My email is Doug at sendpress dot com.
There is also some information on the queue tab under send history. Could you paste that information in the forum? It would probably be a good idea to remove the actual email address when posting that log.