Hidden postbox config options that I find useful. Got o Preferences->Advanced->Config Editor to find them.

pb.conversation_display.max_open_messages

Sets the number of messages that are “Expanded” when you click on a conversation. Setting this to 0 (zero) collapses all the messages in a conversation when you click on it, EXCEPT for the ones that are unread. Makes it easy to see what you haven’t seen before. Default value is 8.

pb.always_mark_as_read

Set this so that when you click on a conversation it doesn’t automatically mark everything as read. NOTE: they recently changed the behavior of this, and it kinda of sucks now … but its still better than the default.

mail.conversation_display.reverse

Toggle this to display the conversations in chronological or reverse chronological order. Personally, i like it so that newest is on the bottom.

mail.thread_without_re

Thread by subject even when there is no “Re:” in the subject; default is false.

mail.strict_threading

Don’t thread by subject; default is false.

mail.correct_threading

Thread things correctly (using References/In-Reply-To) regardless of the order in which messages are added to a folder; default is true.