For incoming mail folders:
Incoming messages will always have a message-id header, so:
1. Convert the OE mailboxes to mboxes with emailchemy
2. The TB mailboxes are already mboxes
3. For each pair of mailboxes to be compared:
	a. grab the OE converted file and the TB file
	b. for both of those, grep -i '^message-id: ' mailboxfile > messageidfile
	c. open each messageidfile thus produced and edit out the message-id: part (as there will be case differences) from each line, leaving only the message id values.
	d. sort each messageidfile
	e. compare. (e.g. vimdiff messageidfile{1,2})

For sent mail:
Sent mail will often not have message-id's (yes, Microsoft and/or emailchemy are stupid about this)
1. Convert the OE mailbox into maildir format (one file per message). emailchemy can do this directly.
2. Convert the TB file to maildir format using
3. now grab the date, recipient, and subject of each message. This will have to do, as there is no unique identifier guaranteed to be in each message. Actually, just timestamps alone will probably work, as it's unlikely you ever sent two messages in the same second. however, to get all three easily, cd into the maildir's "new" component (where dropped the messages) and do this:
(for i in *; do grep -im1 '^Subject: ' $i; grep -im1 '^To: ' $i; grep -im1 '^Date: ' $i; echo 'SEPARATOR'; done) > ../../output
(be sure to grep and make sure no messages contain 'SEPARATOR' in them first :P)
4. Now edit each resulting output file to be broken on SEPARATOR and the message headers are condensed into one line (this will make sorting/comparing easier)
5. clean up differences in format (e.g. OE likes time zones like "PST" whereas TB likes "-0800", etc.)
6. compare

Alternative for sent mail:
as mentioned, just use the dates. to confirm that they're unique enough, just sort unique on each list of dates -- if there are no dupes (it stays the same length after sorting), then it's fine.
you might have to massage the dates into the proper format. OE does weird things with time zones, and daylight saving time might be off by an hour.