For incoming mails that we want to take away from Inbox without any action/response yet.
- inbox2: Use number 2 in sense of "secondary inbox" or "inbox too".
- inbox0: Use number 0 (zero) in sense of "leave no action" or "old/obsolete, expired".
Originally, only "inbox2" was defined for both purposed. Here it is split so that inbox2 can be used for lower priority or "read later", whereas inbox0 is to be skipped. Comparing with GMail's Priority Inbox function which indicates prioritized mails within inbox, "inbox2" label separates low-priority mails from inbox. In addition, the label may be set as "show if unread" and/or prefixed with '.' to place it to upper part of label list.
