This extension securely encrypts/decrypts Gmail™
https://www.boolebox.com/
http://www.redcoolmedia.net/
https://www.lockmagic.com/
https://www.zixcorp.com/solutions/by-deployment/g-suite/
http://grd.me/
https://passlok.com/
https://kodamail.com
https://sendsafely.com
http://www.agentur-simon.de/
Gecko Software
https://www.secure-exchanges.com/
https://www.689cloud.com/