First post here to help other new users.
Thank you Michael and Stefano for this excellent plugin!
I too am using the free version, with SMTP2go’s service.
Ben, like Michael said, my Host also recommended getting away from cPanel/webhost php sending altogether, and use an outside SMTP service.
I did try the free Newsletter SMTP2Go addon, but since I already had the SMTP2Go PLUGIN, I use that for all my wordpress mail handling.
So I deleted the SMTP2Go addon to prevent conflicts, and Newsletter sending now works briskly through the SMTP2Go PLUGIN and their network.
(Btw: I’m using their SMTP2Go free version and they have 24/7 free support. 1000 emails a month free limit, then you pay.)
Colin