#6 Mark all as read

Clicking this button will mark all of your messages as read in the Focused filter or in the Other filter, depending on which you happen to be in. Once clicked, you can revert one or multiple emails to a non-read state by selecting the read email(s), opening the email's options menu by right-clicking on the selected email(s), and choosing Mark as unread:

You can also change email(s) back to unread, clicking on the open menu (...) on the action bar, and choosing Mark as unread or clicking on Mark as unread in the section where emails are displayed: