Mail Directory file format
Info starting with "2,": Each character after the comma is an independent flag.
- Flag "P" (passed): the user has resent/forwarded/bounced this message to someone else.
- Flag "R" (replied): the user has replied to this message.
- Flag "S" (seen): the user has viewed this message, though perhaps he didn't read all the way through it.
- Flag "T" (trashed): the user has moved this message to the trash; the trash will be emptied by a later user action.
- Flag "D" (draft): the user considers this message a draft; toggled at user discretion.
- Flag "F" (flagged): user-defined flag; toggled at user discretion.