I think this issue is due to the new https enforcement. Can you please have a look?
I'll have to pass this onto Sendermen, unfortunately I do not know his current information. Dark kept on saying that when he tried to email him, it would just bounce back, this was a while back though.
@post 1, if 400 The plain HTTP request was sent to HTTPS port - Google Chrome is the error Your talking about, then I'm getting it as well. However, at one point I managed to see some text that said the mail was sent. Weather that's true or not, I don't know.