I don't want to jump excessively into the fray about keywords. However,
my view:
. being compatible with Bayesian filtering technology is important
. $spam should not be used; SPAM is a trademark of Hormel Corp. (a fine
company) for their highly-addictive lunch meat (which goes quite when
when consumed with Dom Perignon)
. $adult has problems. Clearly it is desirable to label crass
pornography, but there's too much of a grey area.
$xxx is a relatively recent convention, to be used for IANA-registered
IMAP keywords which are NOT part of the IMAP specification. In other
words, unlike \xxx flags (which the IMAP software must know about and have
implications in other commands), $xxx keywords are just ordinary keywords
as far as IMAP is concerned.
An existing example is $MDNsent.
-- Mark --
http://staff.washington.edu/mrc
Science does not emerge from voting, party politics, or public debate.
Si vis pacem, para bellum.
