Reason #936 NOT to use “The Cloud”
Reason #1,844 TO use the cloud: security is managed by a third party to ensure they can’t just hack your email.
Managing an email server is NOT easy. They are almost always misconfigured, and a lot of legacy protocols linger in the SMTP stack. With a simple misconfiguration, it would be trivially easy to compromise even an Exchange server.
Microsoft had to turn over information to comply with a secret subpoena. They fought through the courts and eventually disclosed to Project Veritas that they handed over data. It’s their policy to do so.