One of my problems with services that require invitation or entering your email address in any way is that some of these services filter acceptable domain names. Some of them only accept emails from Google, Microsoft, and Yahoo (plus AOL) and that’s a problem for people like me who don’t use these email services for privacy reasons.

I opened an email account on ProtonMail but some of those services didn’t even accept ProtonMail, one of the most famous secure email services. Service providers should stop filtering domain names and email providers.