As far as the software ecosystem is concerned, it is compliant with SMTP, obviously. But if you are going to use an IMAP client, you could as well use any of the zillion email providers that support it, or set up your own mail server.
It's like operating systems. People who want to have it their very specific way use Linux. People who want it to just work out of the box use macOS (but not Catalina).
It's like operating systems. People who want to have it their very specific way use Linux. People who want it to just work out of the box use macOS (but not Catalina).