How is Encryption Actually Used in Public Networks at This Moment?
In relation to email, Google reports regularly on the use of TLS on incoming/outgoing mails through its servers, which is significant sample size given the popularity of GMail. See below.

https://transparencyreport.google.com/safer-email/overview

You can examine the data in quite some detail to see TLS usage by domain, country etc. 

They also see to have other reports on HTTPS usage etc. although I haven’t checked them out myself.