The new version of Yahoo Messenger is redesigned with brand-new features. Now you can share photos instantly, send animated GIFs, and even unsend messages. It's available for Android, iPhone, and on the web via your browser.
On August 5, 2016, legacy versions of Yahoo Messenger will be discontinued.
[versions 11.5 (Windows), 3.0 (Mac), 1.x (Android) and below]
https://yahoo.tumblr.com/post/145715934739/q2-2016-progress-report-on-our-product
https://help.yahoo.com/kb/yahoo-messenger-for-web/SLN26860.html
Yahoo has clarified that it would begin shutting down older versions of Yahoo Messenger on Aug. 5 and will stop working on Aug 31.