> but I really don't find "Hey" a suitable alternatives to Gmail

I don't get why people need an alternative to Gmail. Email is already decentralized. Just buy a custom domain for a few dollars per year, and then use any email provider you want. You'll own your email address forever.

I currently host my email on Protonmail, but if I ever decide to switch providers, I can do it without having to give people a new email address. I could even go back to Gmail. Worst-case scenario is that I lose the old messages in my inbox that I failed to back up, but that's no big deal.