Hah, there's also seznam.cz (meaning "a list") - I wouldn't be surprised if more then half of whole Czech Republic (so ~6M) uses that as their primary mail provider.
It's also a main local web search and maps provider among other stuff, and pretty popular with non-english speaking part of the population.

If the maintainer accepts this they would be most probably killing the project, can't imagine people using it when it drops their user registration by a lot because of blocklists this wide.