Found in script mb2md   (mailbox to maildir)


                if (/^X-Mozilla-Status: ([0-9a-f]{4})/i)
                {
                  $flags .= 'R' if (hex($1) & 0x0001);
                  $flags .= 'A' if (hex($1) & 0x0002);
                  $flags .= 'D' if (hex($1) & 0x0008);
                }
                if(/^X\-Evolution:\s+\w{8}\-(\w{4})/oi)
                {
                    $b = pack("H4", $1); #pack it as 4 digit hex (0x0000)
                    $b = unpack("B32", $b); #unpack into bit string

                    # "usually" only the right most six bits are used
                    # however, I have come across a seventh bit in
                    # about 15 (out of 10,000) messages with this bit
                    # activated.
                    # I have not found any documentation in the source.
                    # If you find out what it does, please let me know.

                    # Notes:
                    #   Evolution 1.4 does mark forwarded messages.
                    #   The sixth bit is to denote an attachment

                    $flags .= 'A' if($b =~ /[01]{15}1/); #replied
                    $flags .= 'D' if($b =~ /[01]{14}1[01]{1}/); #deleted
                    $flags .= 'T' if($b =~ /[01]{13}1[01]{2}/); #draft
                    $flags .= 'F' if($b =~ /[01]{12}1[01]{3}/); #flagged
                    $flags .= 'R' if($b =~ /[01]{11}1[01]{4}/); #seen/read
                }
