I just went through this for a customer and decided I would document it.
I have added the documentation here:
I hope it helps someone else. The hardest part is validating ownership of
the domain if no one has access to the email addresses listed but the
domain registrar. :) That's a whole other process but most should be able
to figure it out.
The one thing to note, at least for namecheap.com, is that the require a
file upload to HTTP, not HTTPS site.
Bradley V. Stone
MAILTOOL Benefit #21 <https://www.bvstools.com/mailtool.html
Product Support - BVSTools has proven over the past 20+ years and working
with thousands of customers all over the world and many different SMTP
servers to have superior support for our products. We feel functionality is
important, but just as important is making sure that emails and phone calls
for support are answered as quickly as possible. During working hours
you'll often get a response in less than 30 minutes.