Email is not secure unless you and the recipient have carefully used encryption.

This has been true ever since email was invented.

It doesn't matter what the TOS /AUP is - that doesn't stop rogue employees creeping trough email. It doesn't matter if they advertise it as a secure sevice or if they use their competitor's advert serving in ads.

We can use words like "wrong", "unethical", "illegal" but that does nothing to make email more secure.

Stop giving your secrets to a 3rd party and being surprised when they know your secrets.