In the most recent versions, XMPie decided to no longer display the
version number in the browser's tab name, but in the Dashboard lower left
corner instead.
Obviously, this won't help you much.
I assume that testing from the Dashboard still works now - I mean: your uProduce IP address, as such, was not blacklisted by SocketLabs?
The only other points that I think, which could make the difference, would be:
* the sender email address (not the "Authentication Required > Login", but the "From > Email" field that you specified in the Dashboard, while testing), vs. the "From > Email" that you specified in Email Template Heder in Circle
* the email body, that contains links (or anything else) that upset your delivery provider. These links can be either your own "business" links (e.g.:
https://bombardier.ca, etc.) or XMPie links such as "Unsubscribe"? If your provider (that I do not know) has a very strict anti-spamming policy, maybe a simple link that points outside the sender domain may make a problem? I would try with a very simple, even non-personalized body
* the presence / absence of a Text body, in addition to the HTML body?
Anyhow, if your investigation in the XMPie Log folders did not help at all, and your delivery provider's tool neither, you may consider asking the XMPie Support Team.