As others have noted they are doing it anyway. Gmail accepts emails from ProtonMail despite "ideological differences" and vice-versa, otherwise it's destined to

As others have noted they are doing it anyway. Gmail accepts emails from ProtonMail despite "ideological differences" and vice-versa, otherwise it's destined to doom. If being separated from the mainstream internet is the reasoning then yeah sure, go ahead, but you also can't complain why no one besides fanatics is using alternatives when the alternatives are not worth using for the mainstream audience.