I think the author is being unintentionally ironic with the title. Windows 10 does have support for all major email providers. The article is claiming it could just as easily have support for niche ones as well.

I really don't know why people are assuming that MS is being malicious -- they support exactly their direct and realistic competitors to Exchange. If the author seriously thinks that 腾讯首页 or Nextcloud, which doesn't even have an email server component, are sapping users from Exchange he's crazy.