Awareness about security is always something challenging, and have good habits in this area is important. Mail encryption was always a technical complex issue, but now it seems to be easy for users. The answer is this German company Whiteout.io
Once you install it, you enter your user and generate a PGP key, the first hurdle you find is the way to differentiate between “0” and “O”.
After the installation some useful e-mails are sent to explain you how the public key and the private key use.
Decrypting is slow for the modern life, to open an light e-mail it takes around 1 or 2 seconds, not bad to me.
You will see a “√” when the message is encrypted.
The organization of same e-mails in a same line (created by gmail) is not available in Whiteout, so you will see all e-mails from the past ordered in a way that does not make sense to you. This should be improved.
Contacts: if you want to have the contact keys of other users in Whiteout.io you have to import their keys. This will enable encrypted e-mails.
Things that works in a similar way to gmail: Folders,