I now have MIMEDefang configured to divert all spamassassin qualified spam to a local user account for manual sorting. I also configured it to copy all other mail to the same account. I then experimented with an Outlook IMAP account to determine when Outlook will mangle the messages. Turns out that simply moving mail between folders in the same IMAP account does not mangle the message, but moving mail to a different account will cause Outlook to rewrite the entire message. Now I just need to figure out how to semi-automate the bayes learning process.