I just made and sent a newsletter but then after some time a checked up on it and it said that 0 emails were sent.
Then after a long time of trying to figure out why the newsletter was not being sent, I finally noticed that there is a small message on the top of the screen when I am inside the Newsletter page that reads:
“The delivery engine is off (it should never be off). Deactivate and reactivate the plugin. Thank you.”
So I deactivated and reactivated the plugin and nothing happened. Also the message was still there.
p.s. on a side note – My humble suggestion is that message should be in a colored box or something so people will notice it.