Почему это электронное письмо, отправленное из Outlook Mobile, отображается как китайские / японские символы в почтовом приложении iPhone?

Я прикрепил реальную цепочку писем ниже, отредактировал и обезличил, насколько это возможно.

UserA отправил письмо UserB. Отправлено с мобильного Outlook на iPhone. UserB пожаловался, что не могут прочитать письмо, утверждая, что оно было на «китайском». UserA зашел в папку «Отправленные» и переслал мне письмо (UserC). Действительно, когда я открывал его в своем приложении для iPhone, текст письма отображался в виде идеограмм (китайский / японский / корейский, не знаю, какие именно).

Я тщательно проверил все настройки как для UserA, так и для UserC, оба являются стандартными настройками для американского и английского языков, без каких-либо настроек иностранного языка. Ни UserA, ни UserC не говорят на каких-либо азиатских языках, и у них никогда не было никаких причин для настройки азиатских языков. UserB не находится под нашим контролем.

Что могло вызвать эту проблему?

Пересылаемое письмо ...

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From: UserA Last Name <UserA@example.com>
To: "UserC@gmail.com" <UserC@gmail.com>
Subject: Fwd: Showing tomorrow is confirmed
Thread-Topic: Showing tomorrow is confirmed
Thread-Index: AQHUh41jXBWkwhOAEkqLJ6K9zd8oDKVnuH4A
Date: Fri, 30 Nov 2018 04:18:54 +0000
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UserA Last Name | Realtor =AE
... redacted ...
________________________________
From: UserA Last Name
Sent: Wednesday, November 28, 2018 6:47:44 PM
To: UserB Last
Subject: Showing tomorrow is confirmed

Hi UserB,
We are confirmed to see both properties tomorrow. I will see you tomorrow, =
Thursday at 12 pm at Main street. We will see 2nd Street right after. Pleas=
e let me know you received this email. Thank you! :)
UserA

UserA 
... redacted ...

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<b>Sent:</b> Wednesday, November 28, 2018 6:47:44 PM<br>
<b>To:</b> UserB Last<br>
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