Author odo2
Recipients barry, maxking, mjpieters, odo2, r.david.murray
Date 2020-08-06.18:13:34
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Further, under Python 3.8 the issue is not fully solved, as other identification headers are still being folded in a non-RFC-conformant manner (see OP for RFC references). This was indicated on the original PR by the author:

It is less severe of a problem than for Message-ID, but still means that MTA/MUA may fail to recognize the threading structure because identifiers are lost.

Is it better to open a new issue for this?

# Example on 3.8.2: the `In-Reply-To` header is RFC2047-folded.

Python 3.8.2 (default, Jul 16 2020, 14:00:26) 
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import email.message
>>> import email.policy
>>> msg = email.message.EmailMessage(policy=email.policy.SMTP)
>>> msg['Message-Id'] = '<">>'
>>> msg['In-Reply-To'] = '<">>'
>>> print(msg.as_string())
Message-Id: <">>
In-Reply-To: =?utf-8?q?=3C92922734221723=2E1596730568=2E324691772460444-anot?=
Date User Action Args
2020-08-06 18:13:34odo2setrecipients: + odo2, barry, mjpieters, r.david.murray, maxking
2020-08-06 18:13:34odo2setmessageid: <>
2020-08-06 18:13:34odo2linkissue35805 messages
2020-08-06 18:13:34odo2create