A new “Archive” button has been added to the ribbon in Outlook:
Note, this Archive button has absolutely nothing to do with Outlook’s archive functionality. This new button is simply doing a move of whatever items are selected. So, if you’re in the habit of dragging messages into a folder when you don’t want to see them in the main folder any longer, you can use this button instead to accomplish the same thing.
Outlook Online also has an archive button, which does the same thing as the Outlook Client:
Where do “archived” messages go?
By default, they’ll land in a folder named “Archive” which shows up as a top level folder:
How to change which folder is used?
In the Outlook Client, go to File –> Tools –> Set Archive Folder…
Changing the folder will take effect immediately in the Outlook Client, and will sync to Outlook online and take effect there in about 15 minutes.
One more difference between Outlook Client and Outlook Online: keyboard shortcuts. In the client you can archive items via backspace, in Outlook online it’s “e”.