readmail.py

#!/usr/bin/env python3

import sys
import email
from email.policy import default

class MboxReader:
    def __init__(self, filename):
        self.handle = open(filename, 'rb')
        assert self.handle.readline().startswith(b'From ')

    def __enter__(self):
        return self

    def __exit__(self, exc_type, exc_value, exc_traceback):
        self.handle.close()

    def __iter__(self):
        return iter(self.__next__())

    def __next__(self):
        lines = []
        while True:
            line = self.handle.readline()
            if line == b'' or line.startswith(b'From '):
                #yield email.message_from_bytes(b''.join(lines), policy=default)
                if line == b'':
                    break
                lines = []
                continue
            lines.append(line)


i=0
with MboxReader(sys.argv[1]) as mbox:
	for message in mbox:
		print(sys.argv[1], '-', i, ':', message.as_string())
		i=i+1