Many mail clients have the option of marking an outgoing message 'high priority' or 'urgent.' In Mail.app, such messages show up in the Inbox with two exclamation marks (!!) in the flags column. If you want to sort messages by the flags column, so that messages you flag yourself are at the top, all high priority messages you have ever received will also be at the top of the inbox.
Mail.app currently has no way of removing this flag from emails you have received (as noted in
this Apple discussions thread.). The following shell script allows you to unset the priority status of
all the emails you have ever received, so that no emails in your inbox have '!!' next to them any more:
sqlite3 ~/Library/Mail/'Envelope Index' 'update messages set flags = flags | 196608 where flags & 196608 != 196608;'
You can save this as an AppleScript by opening AppleScript Editor and entering the following:
do shell script "sqlite3 ~/Library/Mail/'Envelope Index' 'update messages set flags = flags | 196608 where flags & 196608 != 196608;'"
Save this and run it whenever you get High Priority emails (check out FastScripts to make this easy) to make them normal priority again, so that you can flag what you think is important instead of the sender.
[
crarko adds: I tested this, and it works as described. This has been an annoyance about Mail so it's nice to have a way to fix it.]