Yes
If so, then the status of the message is stored
in the filename, not in the file. See
http://cr.yp.to/proto/maildir.html in the section "What can I put in
info?" to see the status format.
Yes, I've noticed the ':2S' (I think that's right), where the 'S'
indicates a message has been seen.
That said, I don't think there is any way to directly access or
manipulate those flags from within Maildrop.
That really doesn't seem to be what the documentation for the KEYWORDS
variable seems to indicate.
"The KEYWORDS variable is used only when delivering a message to a
maildir, and implements the optional IMAP keyword extension as
implemented in the Courier-IMAP. It may be optionally initialized to
contain a comma-separate list of keywords."
From that I would at least expect the courierimapkeywords directory
would be filling with entries. The fact that it is not, indicates to me
that either the KEYWORDS variable is depreciated, not working, or (more
likely) I have an incorrect configuration.