Trying to move to more secure emailing. But is it pointless if my contacts don't also use secure client?

I have 3 use cases I want to solve, coming from gmail and separately an own domain email (routed currently via email):

* Move from single email address to several aliases for obfuscating across vendors using data collection (for credit cards, I'd use at least a few virtual card numbers)
* One single front-end client to read and send emails from aliases
* Choosing a secure email client which can't snoop my messages

But I am not sure if this …

client contacts don privacy