Help with spam

I just started using Proton as mail provider. I've got a custom domain for a small business website but it is not fully functional yet. Just a landing page with a Contact Us box.

Almost immediately after getting set up, I started receiving obvious spam messages to my email. Which is weird since I don't list the email address anywhere on the site yet. It is just "Info@(customdomain).com also these messages are not running through the Contact Us box because that shows up as a specific format. These are just sent straight to my (so far unlisted) email address.

The messages are all from weird names with gmail addresses, who appear to not speak english very well. It's often something like "may I please speak to the store owner please?" or "are you still taking orders?" Usually with no subject line. And it almost always lists my email address in the body of the message for some reason.

At this point Proton is getting good at sending them all to spam. But I'm wondering if there is anything else I can do to stop them, or how they even started in the first place.