Earlier quoted context omitted.
There's little need to nationalize, since emails don't have a last-mile or natural monopoly issue. I think, however, that modern countries should provide all citizens with an official, public, mail address. Restrict them to only send/receive emails to/from a whitelist of publicly registered service providers with very strict personal data governance requirements (government, banks, utilities, medical services, higher…
Good idea which will work for most people, however it'll be an issue for dissidents or people moving countries. Those can use some other provider, while everyone else (99%?) can be covered by this solution. I guess there should be a provision against gov services making it mandatory for people to use the gov provided email.
In my view those email address should be strictly national and reserved for national-level services, so whenever you move to another country you should get a new email address at the same time as you get a tax ID number.