To: test@example.com
From: test@example.com
Subject: ISO-2022-JP and 7bit containing =67 and hence looking like quoted-printable
Message-ID: <10a2aa17-e92f-417c-864e-575d4e371702@example.com>
Date: Tue, 3 Apr 2018 19:09:16 +0900
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.6.0
MIME-Version: 1.0
Content-Type: text/plain; charset=ISO-2022-JP; format=flowed
Content-Language: ja-JP
Content-Transfer-Encoding: 7bit

現況