Status: O
---------
MC: UNIX mail reading programs which open a traditional UNIX format mailbox
    set all existing messages to have "O" (old) status.  This is interpreted
    by Pine as meaning "not recent" ("recent" is an IMAP concept, and Pine is
    based upon an IMAP used with IMAP).  Note that this is not the same as
    "seen", which is governed by the "R" status flag.

As soon as you open a _remote_ stream/mailbox in any other way than HALF_OPEN c-client
will attach an "old" flag to the message.

As soon as you write to an open _local_ stream/mailbox c-client will attach an "old"
flag to the message.

Status: R
---------
Seen - this means that the user has actually _looked_ at the message. This flag can be set
and removed.

Sources:
--------
http://www.washington.edu/pine/pine-info/2004.01/msg00061.html
