Common email providers tend to allow (or require) a secure HTTPS connection between the browser or email client and their servers. It’s great that the message is safely transported from your browser to the mail server, but unless it’s intended for someone else using the same server, it must travel across the public Internet. Large enterprises solve the “library” problem by setting up a Certificate Authority – a service that manages the keys – and configuring every computer within the business to trust that service. Keybase is an attempt to make encryption encryption accessible to the average user.”]
Source: https://www.csoonline.com/article/2931491/how-secure-is-your-email.html