www.makemkv.com

I tried to create an account using my standard email address (ending in @proton.me), but the site wouldn't accept it. However, I was able to use a random temporary-email-provider. Afer I created this account I tried changing it in the User Control Panel, but had no luck either, which is unfortunate since I will eventually lose access to the temporary email.
Is Proton-Mail banned, or did I do something wrong?

Yes, proton.me is one of several domains blocked for past spam activity. Quite a few proton.me users instantly started posting spam messages, to the point where the domain was finally blocked.

It is unfortunate for the people who find a legitimate reason to use them, but you're actually the first person to ask about it since the domain was banned several years ago.

Unlucky. Thanks for the response, though.