This is the singular reason I have chosen their primary competitors over them. In this day & age you need to be aware of these details.
The thing is - email isn't just sitting in your mailbox to only be viewed by you. The recipient has a copy which could leak it (or via hax). Copies of email can be saved by both incoming and outgoing systems.
If you need security & privacy - email is not the technology you want to use whatsoever.
Overall happy with the service. Customer support has answered questions competently.
If PM is not a honeypot, they are incompetent.