AppleScript - extract an email message as a MIME object

I have an AppleScript I wrote to do some parsing on Mail.app messages, however it seems I will need more powerful processing (specifically - separate a replied message from the original message it quotes) than what is provided by AppleScript (say, using Python's email package). Is it possible to get an email message as a MIME string?

I'm not sure if this is what you meant, but here is how you can get the raw message text from a selection you've made in Mail.app which can than be processed with MIME tools to extract all the parts.

tell application "Mail"
    set msgs to selection
    if length of msgs is not 0 then
        repeat with msg in msgs

            set messageSource to source of msg

            set textFile to "/Users/harley/Desktop/foo.txt"

            set myFile to open for access textFile with write permission
            write messageSource to myFile
            close access myFile

        end repeat
    end if
end tell

And then here's a Python email example script that unpacks the message and writes out each MIME part to a separate file in a directory

https://docs.python.org/3.4/library/email-examples.html

#!/usr/bin/env python3

"""Unpack a MIME message into a directory of files."""

import os
import sys
import email
import errno
import mimetypes

from argparse import ArgumentParser


def main():
    parser = ArgumentParser(description="""\
Unpack a MIME message into a directory of files.
""")
    parser.add_argument('-d', '--directory', required=True,
                        help="""Unpack the MIME message into the named
                        directory, which will be created if it doesn't already
                        exist.""")
    parser.add_argument('msgfile')
    args = parser.parse_args()

    with open(args.msgfile) as fp:
        msg = email.message_from_file(fp)

    try:
        os.mkdir(args.directory)
    except FileExistsError:
        pass

    counter = 1
    for part in msg.walk():
        # multipart/* are just containers
        if part.get_content_maintype() == 'multipart':
            continue
        # Applications should really sanitize the given filename so that an
        # email message can't be used to overwrite important files
        filename = part.get_filename()
        if not filename:
            ext = mimetypes.guess_extension(part.get_content_type())
            if not ext:
                # Use a generic bag-of-bits extension
                ext = '.bin'
            filename = 'part-%03d%s' % (counter, ext)
        counter += 1
        with open(os.path.join(args.directory, filename), 'wb') as fp:
            fp.write(part.get_payload(decode=True))


if __name__ == '__main__':
    main()

So then if the unpack.py script is run on the AppleScript output...

python unpack.py -d OUTPUT ./foo.txt 

You get a directory with the MIME parts separated. When I run this on a message which quotes an original message then the original message shows up in a separate part.