I work for Virtru (https://www.virtru.com/get-secure-email), which allows you to send encrypted email from your existing email address (e.g. gmail). I use it daily for testing, but I use it at least weekly for actual use cases. For example, emailing my roommate a shared password, emailing sensitive business information, or simply sending messages to a friend which I don't want sitting on a 3rd party server in plain text.