Mailbox has been updated to version 1.7, adding support for iCloud and Yahoo! Mail accounts. Mailbox does not yet support mail aliases from non-Gmail accounts, however. There are a number of other improvements as well, including the return of background sync. You can now also disable the "Help Me Get to Zero" banner that appears in the app. There is another option to disable swiping to open the drawer. Since you can swipe to open the drawer from any point on the screen, disabling the feature prevents you from accidentally archiving messages.
You can download this update right now from the App Store.