You had nothing in the “Send email from” field. Mail server requirements vary. Some will accept the default “[email protected]” but these days most will not. I added your email address there and now it works.
I am pretty sure that this fixed what I thought was a major issue, I could not figure out a way to add a new user. I started in the back end with “approval by admin” and when I hit save I got a blank screen. So I tried the front end requesting to register and ended up a a blank screen with the menu at the top.
I have forgotten all my machinations now, I believe it included trying to use the contact button at the bottom.
But putting in a valid “from” email address has adding a user (approving the first one I tried 3 times before) working!!