The following proglet gets an except with the attached
message:
-----te.py--------
import email
import sys

msg = email.message_from_file(sys.stdin)
sys.stdout.write(msg.as_string())
------------------
python2 te.py <failingmsg
Traceback (most recent call last):
  File "te.py", line 4, in ?
    msg = email.message_from_file(sys.stdin)
  File "/usr/lib/python2.2/email/__init__.py", line 63,
in message_from_file
    return Parser(_class, strict=strict).parse(fp)
  File "/usr/lib/python2.2/email/Parser.py", line 64,
in parse
    self._parsebody(root, fp, firstbodyline)
  File "/usr/lib/python2.2/email/Parser.py", line 239,
in _parsebody
    msgobj = self.parsestr(part)
  File "/usr/lib/python2.2/email/Parser.py", line 75,
in parsestr
    return self.parse(StringIO(text),
headersonly=headersonly)
  File "/usr/lib/python2.2/email/Parser.py", line 64,
in parse
    self._parsebody(root, fp, firstbodyline)
  File "/usr/lib/python2.2/email/Parser.py", line 264,
in _parsebody
    msg = self.parse(fp)
  File "/usr/lib/python2.2/email/Parser.py", line 64,
in parse
    self._parsebody(root, fp, firstbodyline)
  File "/usr/lib/python2.2/email/Parser.py", line 205,
in _parsebody
    raise Errors.BoundaryError(
email.Errors.BoundaryError: No terminating boundary and
no trailing empty line
-------------------
The message/rfc822 attachment really is missing the
boundary.  However, that is why it is being returned as
an attachment in the first place!  Is it illegal for
message/rfc822 attachments to have invalid MIME
construction?

I suggest that a message attachment that fails MIME
boundary decoding, should become a plain rfc822 object,
or perhaps a text object.  I don't know.  

Anyway, I get tons of messages with this property that
have to be processed by my Python milter.

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I'm moving this to a feature request for Python 2.4. 
There's little that we can do about this in Python 2.3 since
the lax parser is only so good at guessing the intent of
ill-formed messages.  email 2.x can't do what you suggest
because that would be a new feature and can't be introduced
into Python 2.3.  The email-sig is chartered with developing
an improved parser for Python 2.4 that might be able to
handle this.

In the meantime, you could probably derive your own Parser
class that might be able to worm around this problem in an
application specific way.

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user_id=142072

Your disposition makes sense.

Since all messages with invalid MIME boundaries are either
invalid themselves, or bounces or forwards of invalid
messages, my work around is to issue an SMTP reject:

      if exc_type == email.Errors.BoundaryError:
        self.setreply('554','5.7.7',
                'Boundary error in your message, are you a
spammer?')

For 2.4, I recommend that rfc822 attachments be parsed
independently of the enclosing message.  If the attachment
is invalid, turn it into a plain rfc822 message object or a
string.

Although the rfc822 module is deprecated, I find it very
useful to represent mail that may or may not correctly
follow MIME standards.   Examples include forwarded spam
(using the new innoculation RFC), and generic mailbox
processing.  I suggest retaining rfc822 as a 'featureless'
message with only headers and body.

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Note that if you're looking for something that just parses
messages into headers and bodies, you might look at the
HeaderParser class.  You'd have to write a bit of code to
get an outer parser that falls back to a HeaderParser on
invalid unparseable inner messages.

I don't see any exception as of Python 2.5. Closing as "fixed".