The biggest update is that Yahoo Mail will now let you access email from other account providers through the Yahoo Mail app. Users will now be able to connect mail accounts from Outlook.com, Hotmail and AOL to Yahoo Mail. BUT…not to Gmail.

As for passwords,

Yahoo vice president of product Dylan Casey says that passwords and even security questions are an antiquated solution for protecting Web users…

“To rectify that broken authentication system, Yahoo is killing off passwords in its latest release. Through a new feature called Account Key, users can choose to prove their identity by way of a push notification sent to their phone. The notification ask users if they’re trying to log into their account. Pressing ‘yes’ allows access to the account, pressing ‘non’ denies it.

This new feature builds on a product the company release earlier this year called on-demand passwords, a two-factor authentication like experience where Yahoo emails a new password to your phone.” – Dylan Casey

Read more here: http://venturebeat.com/2015/10/15/yahoo-mail-will-now-let-you-access-multiple-third-party-mailboxes-in-lastest-overhaul/