I've read the other incident reports about failure to send where the resolution appeared to be increasing the max limit of outbound emails permitted by the hosting server.
Based on that, I've been having calls with my hosting service, and they have bumped my limit 3 times... to the point where I am now almost 4x the number of recipients for the email... and it is still failing to connect.
The hosting provider has checked the email log files and can't find anything on the logs indicating any form of error.
All attempts to send the exact same contents and the same header to 1-5 users works fine. My overall Member list is 120+... and it chokes every time. My limit is now up to 750 and it is still not "instantiating".