Ideas

Address Book

• improve layout

wwp: I'd propose to (optionally) embed/dock the edit dialog contents into the AB window, as it wouldn't require to enlarge the size of the dialog too much (the layout you're proposing, Hoa, requires much more space on screen, and here it can't fit). See: editing user info [1], editing group members [2].

• use vcard ?
• make it a separate application ?

Preferences

• in account configuration, hide advanced option so that basic options are all under the same tab

Message List

• collapsed thread selection
  • when clicking on a collapsed thread (for example, when clicking on the subject) => expand all the thread
  • when the thread is collapsed and selected, consider all the thread is selected