What’s more, having people actually use and pay for your product is much better validation than people saying they will (not always the same thing)
Today, we have much better spam filters, companies realizing sending unwanted spam only hurts them (so they offer unsub), and password managers.
I would signup for a product just to see more info if I was curious about their offering.
I trust that at absolute worst I can email MailChimp and they will actually act on my desire to unsubscribe, and I know that almost certainly that won't be needed because of their enforcement of reasonable unsubscribe.
I find it ironic because it seems they wanted as anodyne a domain as possible so they wouldn't clash with their customers' brands.
But yeah, of course, having people actually use and pay for your product is the ultimate validation.