Email isn't private. It was designed to be robust not private. Encryption never really caught on; and your counterparties using Gmail or some Microsoft server in the background will kill any expectation of privacy you might have.
WW II's Gordon Welchman is worth reading about. Similar nasty end as Turing. Not as well known as Turing but a similar contribution before the encryption was actually solved.
Have used Zoho for decades. Dozen domains, three/four actual accounts. Don't seem to have had any issues with them selling my info - use them with Addy.io. I don't gain anything from this reference/comment.
[ Suddenly the whole of London's property market crashes as tens of thousands of houses owned by faceless corporations owned by charities suddenly appear on the market at fractions of their values just before it is announced. ]