It would be great to have the Archive button not just in the context menu of mails, but als on folders. It would be great to be able to archive all mails in all sub-folders.
Also just from a UX point of few when I tried to archive mails for the first time the folder context menu was also where I initially looked for. When I didn't find it there I googled how to enable archiving just to find out that it is in the context menu of the emails.