I've got a domain, and I'm wondering why this "catch-all" thing is grayed out.

I have this domain which I am using to route email, and I saw people mention this danged thing, and it seems so useful to me, but I'm afraid to do so much as click it to find out what'll happen. The only assistance I ask is what clicking this entails, as I am afraid of anything unexpected occurring suddenly with my wallet. I am using the free tier, and I have a .com domain, if that helps with context any.
image.png
Was this page helpful?