Column headings in Windows Mail

I'm in the process of setting up Windows Mail and transferring from Outlook
Express 6.

I must say I'm disappointed with what I've seen so far in Windows Mail Help.
When I put in a search term, it appears to search all of the Windows Help
database, rather than just the Windows Mail database -- can make it a lot
harder to find the right place if the search term is also used elsewhere in
Windows with a different meaning.

There are 3 column headings in Windows Mail for which I can find no
explanation in Help -- Rank, Msg Type and Rating. If they are explained
somewhere in Help, can someone point me to the place? Otherwise, can
someone tell me what they mean and their purpose?

Thanks

Lindsay Graham