Yahoo is rolling out an option that will help protect users privacy when accessing their web-based email. Without HTTPS, emails are sent as unencrypted text and transmitted to your browser. Yahoo has made the HTTPS/SSL setting disabled by default, meaning users are required to turn it on. Hopefully in time, Yahoo will decide to enable the option by default as it is with Gmail, Hotmail and Outlook.com. It’s too much to hope that AOL might be the next to implement a HTTPS option for its email service.”]
Source: https://nakedsecurity.sophos.com/2013/01/08/yahoo-mail-https-ssl/