This encryption plug-in for Yahoo mail is going to be welcomed by many. I know quite a few people that use yahoo mail, and some prefer it over gmail.

While at this stage we’re rolling out the source code for feedback from the wider security industry, our goal is to provide an intuitive e2e encryption solution for all users by the end of the year. Yahoo Demonstrates End-To-End Email Encryption Plugin [yahoo.tumblr.com]

we’ve released the first Yahoo specific e2e encryption plug-in source code on GitHub.

Here's the source code link [github.com...]

Here's Yahoo's demonstration video [youtube.com...]