EmailMessage bad encoding for international domain

[Julien00859]

BPO	39757
Nosy	@warsaw, @bitdancer, @Julien00859, @iritkatriel
PRs	bpo-39757: Use IDNA to encode domain part in email address #18667

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-02-26.09:36:15.270>
labels = ['3.11', 'type-bug', 'expert-email', '3.10', '3.9']
title = 'EmailMessage bad encoding for international domain'
updated_at = <Date 2021-12-13.17:50:29.456>
user = 'https://github.com/Julien00859'

bugs.python.org fields:

activity = <Date 2021-12-13.17:50:29.456>
actor = 'iritkatriel'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['email']
creation = <Date 2020-02-26.09:36:15.270>
creator = 'Julien Castiaux'
dependencies = []
files = []
hgrepos = []
issue_num = 39757
keywords = ['patch']
message_count = 5.0
messages = ['362687', '362801', '362802', '362906', '408472']
nosy_count = 4.0
nosy_names = ['barry', 'r.david.murray', 'Julien Castiaux', 'iritkatriel']
pr_nums = ['18667']
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue39757'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']

Linked PRs

• gh-83938, gh-122476: Stop incorrectly RFC 2047 encoding non-ASCII email addresses #122540

[Julien00859]

Affected python version: 3.5 and above (did test them all except 3.9)

Steps to reproduce:

  from mail.message import EmailMessage
  from mail.policy import SMTP

  msg = EmailMessage(policy=SMTP)
  msg['To'] = 'Joe <joe@examplé.com>'  # notice the é in the domain
  print(msg.as_string())

It prints

To: "Joe <joe@=?utf-8?q?exampl=C3=A9?=.com>"

But it should be

To: "Joe <joe@xn--exampl-gva.com>"

While b64/qp can be used to encode most non-ascii headers, the domain part of an email address is an exception. According to IDNA2008 (rfc5890 , rfc5891), non-ascii domain should be encoded using the punycode algorithm and the ACE prefix.

[Julien00859]

Duplicate of https://bugs.python.org/issue39757

[Julien00859]

Woops wrong copie/paste, here is the correct link: https://bugs.python.org/issue11783

[bitdancer]

This is not actually a duplicate of 11783. Rereading (parts of) that issue, we decided we currently have no good way to do automatic conversion between unicode and internationalized domains, so the user of the library has to do it themselves. This means that the bug *here* is that the new email API is *wrongly* encoding the non-ascii in the domain by using an encoded word. I'm surprised at that; I thought I'd guarded against it.

What should be happening here is that an error should be raised when that header is set (or possibly when it is accessed/serialized, but when set would be better I think) saying that there is non-ascii in the domain part.

[iritkatriel]

Reproduced on 3.11.