Jeremy, thanks for replying. It's good to see that level of support! But I think my solution is just to stick with the clean-and-simple-contact-form that works out-of-the box.
You can check if that function works properly by leaving a comment on your site and checking if you receive an email.
I do. It has been the case throughout.
you could use a plugin like this one to configure your WordPress installation to use a specific email service
Okay, but it's apparently simpler to use the clean-and-simple-contact-form plugin I set up yesterday.
If the function appears to be work properly, ...
This sounds useful if I devote the time to puzzling it out. Chasing my ISP, setting up alternative emails and so on are good to know about should the alternative plugin stop working. But I can't see the justification for taking the time to do all that just now.
you can deactivate Jetpack's Contact Form by following the instructions here.
I had already deactivated it before Jorge mentioned it. He seems to have missed that bit. Jetpack is still installed and active.