Source: : https://techcommunity.microsoft.com/t5/Office-365-Groups/New-Drag-and-drop-conversations-into-groups/m-p/124722#M4410

Good news! We’re currently rolling out drag and drop for messages and conversations into groups in Outlook on the web first for First Release customers, then Standard release customers.

It’s much easier to explain with a GIF:

 

Support for Outlook 2016 for Windows is coming soon–stay tuned.

You can find the documentation here: https://support.office.com/en-us/article/24e809db-70e1-45b7-8d54-efac7951dc95

The latest set of updates for Groups in Outlook introduces new ways to manage the group emails you receive in your inbox. These updates are, in large part, based on customer feedback about the Groups subscription model. That model has now been replaced with Follow in inbox.

https://techcommunity.microsoft.com/t5/Outlook-Blog/Introducing-Follow-in-inbox-and-other-improvements-for-managing/ba-p/102611

 

 

 

https://blogs.technet.microsoft.com/enterprisemobility/2017/08/09/automated-expiration-for-office-365-groups-using-azure-ad-is-now-in-public-preview/