[labria]

And what about the "Reference"? IMO, not all emails are tasks, some of them are just data to be stored. What should I do with those?

[andymitchell]

Exactly, so today's email client broadly serves two functions: 1) to manage emails (which is to say, manage the flow of tasks that emails represent), 2) be a knowledge base.

Reference labels are essentially meta data - so you might create a general reference labels for invoices, receipts, meeting notes, etc. You can then use ActiveInbox's sidebar menu to drill into the knowledge base -> look for meeting notes for a given project, or invoices for a given contact.