@crazycells great topic. PGP has been around for years, and it’s predecessor (if memory serves me correctly) was World Secure. As I’ve said countless times to many people, email is not a secure transport by default, therefore, unless you’ve taken steps to secure (encrypt) the traffic stream, you should not expect any level of privacy.
PGP works well but requires Public Key Encryption in order to work. Using symmetric and asymmetric algorithms plus an array of proxying, there are no known ways of breaking it. However, PGP itself was acquired some time ago by Symantec, so if you want to go the truly open source (FOSS) route, you’ll need OpenPGP.
The huge advantage of PGP is it’s ability to send a message without needing to share any form of keys, so if you’ve never met the recipient, you can still send a message and have it completely secured in transit.
Being the huge privacy advocate that I am, I’m a big supporter of anything like this.
As a final note, Proton Mail is well worth a look, and with a paid subscription, you can incorporate your own domain email.