How to remove your Yandex mail account
Be logged in and use the removal link named here.
Direct removal link: https://passport.yandex.com/passport?mode=delete
Helpful Trick: Removing online data
Helpful Trick: Remove third-party logins
If you signed up for Yandex mail using a third-party login such as Facebook or Twitter, you probably want to revoke all access from Yandex mail. Click here to find out how.