オリジナル版だと2byte文字のデコードができないっぽいことがあったので一回decode_headerをかました

parseml.py

#!/usr/bin/env python

"""
2020 update:
- More iterators, fewer lists
- Python 3 compatible
- Processes files in parallel
(one thread per CPU, but that's not really how it works)
"""

import email
import glob
import os
from email.header import decode_header
from multiprocessing import Pool

EXTENSION = "eml"


def extract(filename):
    """
    Try to extract the attachments from all files in cwd
    """
    # ensure that an output dir exists
    od = "output"
    os.path.exists(od) or os.makedirs(od)
    output_count = 0
    try:
        with open(filename, "r") as f:
            msg = email.message_from_file(f)
            for attachment in msg.get_payload()[1:]:
                raw_attachment_name = attachment.get_filename()
                # If no attachments are found, skip this file
                if raw_attachment_name:
                    files = decode_header(raw_attachment_name)
                    byte_attachment_name, encoding = files[0]
                    decoded_attachment_name = byte_attachment_name.decode() \
                        if type(byte_attachment_name) == bytes \
                        else byte_attachment_name
                    with open(os.path.join(od, decoded_attachment_name), "wb") as of:
                        of.write(attachment.get_payload(decode=True))
                        output_count += 1
            if output_count == 0:
                print("No attachment found for file %s!" % f.name)
    # this should catch read and write errors
    except IOError:
        print("Problem with %s or one of its attachments!" % f.name)
    return 1, output_count


if __name__ == "__main__":
    # let's do this in parallel, using cpu count as number of threads
    pool = Pool(None)
    res = pool.map(extract, glob.iglob("*.%s" % EXTENSION))
    # need these if we use _async
    pool.close()
    pool.join()
    # 2-element list holding number of files, number of attachments
    numfiles = [sum(i) for i in zip(*res)]
    print("Done: Processed {} files with {} attachments.".format(*numfiles))