[Design] Which inbound changes should be considered/ignored for marking an item unread or moving to the NOW section

[Morgen Sagen]

I filed a bug *** on myself to track the need for a mechanism which
would allow certain inbound changes to be ignored when determining
whether an item should be marked unread or moved to the NOW section.
Mimi asked me to move the requirements discussion of this bug to the
design list.  See the bug report for the list of fields that are
shared, and let me know which of these should be ignored.

*** https://bugzilla.osafoundation.org/show_bug.cgi?id=10799