I'm trying to track down where message uid is encoded in a message in a mbx mail folder?
In general, you should not worry about the format of an mbx mailbox unless you need to repair one. In particular, you should use the c-client library to access mbx mailboxes and not write your own code to do so; the mbx mailbox locking protocol is quite complex and it is easy to make a mistake.
The UID is stored in the per-message line as the last field (following the hyphen). That is, with a per-message-line of:
16-Mar-2000 00:51:24 -0800,6726;000000100009-0000087b
INTERNALDATE: 16-Mar-2000 00:51:24 -0800 RFC822.SIZE: 6726 FLAGS: 000000100009 UID: 0000087b
-- Mark --
http://staff.washington.edu/mrc Science does not emerge from voting, party politics, or public debate. Si vis pacem, para bellum.