What version of powermessenger are you using?
I think the spam testing service we had integrated may have stopped doing spam checks.
One solution would be to use this service: https://www.mail-tester.com/
Get the email address and send a test email to it and then you can check the spam score.
If you have a low spam score, but your email is still flagged as spam... another possible reason for delivery failure is the lack of proper SPF and DKIM settings on the mailing server itself. That is a server configuration thing you can talk to your hosting company about since it can vary slightly depending on who you host with.
Here is an article for how to do it on GoDaddy: http://support.postmarkapp.com/customer/portal/articles/64737-adding-dkim-and-spf-records-to-go-daddy