When parsing a (broken) mail from linux-media@vger.kernel.org (message-id 20190212181908.Horde.pEiGHvV2KHy9EkUy8TA8D1o@webmail.your-server.de, headers attached) with email.policy.SMTP, I get an AttributeError on trying to read the 'to' header:

/usr/lib/python3.7/email/headerregistry.py in <listcomp>(.0)
    345                                              mb.local_part or '',
    346                                              mb.domain or '')
--> 347                                      for mb in addr.all_mailboxes]))
    348             defects = list(address_list.all_defects)
    349         else:

AttributeError: 'Group' object has no attribute 'local_part'

The header in question is:
To:     unlisted-recipients:; (no To-header on input)

The problem seems to be that mb is a Group and not an Address, gets token_type of 'invalid-mailbox', but does not have the attributes local_part/domain that are expected in mailboxes. Copying the line

local_part = domain = route = addr_spec = display_name

from InvalidMailbox to Group fixes this, but it is not clear to me this is the right solution, so not sending a patch.

Anton: thanks for the report! In the message you say you are not sure of the solution, and because of that not sending a patch, but then you created the PR; - please clarify.

How are you encountering this error?  The following program runs without exception for me on master:

from email import message_from_binary_file
from email.policy import SMTP

msg = message_from_binary_file(open('mail.eml', 'rb'), policy=SMTP)
print(msg)

Running R.David's test script on python3.7, it also works, there's no exception.

I should have been more exact - I've used python3.7.7 .

Quoting R. David Murray (2021-07-06 18:59:56)
> How are you encountering this error?  The following program runs without exception for me on master:
> 
> from email import message_from_binary_file
> from email.policy import SMTP
> 
> msg = message_from_binary_file(open('mail.eml', 'rb'), policy=SMTP)
> print(msg)

The exception is thrown on accessing the 'to' header, so make that
print(msg['to'])

Quoting Andrei Kulakov (2021-07-03 16:03:34)
> Anton: thanks for the report! In the message you say you are not sure
> of the solution, and because of that not sending a patch, but then you
> created the PR; - please clarify.

I didn't send a patch when originally submitting the bugreport in 2019.
I did write a patch about a year later, since there was no response to
the bugreport.

Ping yet again. Can anyone please look at this?

I confirmed I get the same error as Anton on 3.9 and 3.11 .