mail views are built on top of quick search and the search code
the user can customize their views. the view info is saved to a file named mailViews.dat
for this feature the search backend had to be modified to support mixed AND/OR searches. This is not visible in the UI.
for more details, see http://bugzilla.mozilla.org/show_bug.cgi?id=171073
for this feature the search backend and front end had to be modified to support junk status searches, label searches, age in days searches, and has attachment searches.
UI spec: http://www.mozilla.org/mailnews/specs/views/