>>I don't see what the prefixes accomplish

 MR> They're for users who don't use filters and dump all their
 MR> mail into one inbox unfiltered.

not necessarially... my filtering software makes use of it to determine
which  "friend" it is that sent the mail so that it isn't marked
as spam...

my mail reader uses them to know which folder to move them to on inbound to
the local inbox and then another filter uses them to know which folder to
move them to after they've been read...

JFWIW, ya know ;)

)\/(ark