使用imap 奇怪的问题

使用imap收取邮件是，某一用户 会收到  发件人空白的邮件 主题 なし （日文版office）。

邮件内容部分如下：

Received: from xxxxx.com.cn (192.168.1.2) by
 xxxxxxx.com.cn (192.168.1.2) with Microsoft SMTP Server (TLS)
 id 15.12.396.30 via Mailbox Transport; Wed, 4 Jul 2018 16:51:57 +0800
Received: from xxxxxxx.com.cn (192.168.1.2) by
 xxxxxxx.com.cn (192.168.1.242) with Microsoft SMTP Server (TLS)
 id 15.12.396.30; Wed, 4 Jul 2018 16:51:57 +0800
Received: from xxxxxxx.com.cn ([::1]) by
 xxxxxxxxxx.com.cn ([::1]) with mapi id 15.01.0396.037; Wed, 4 Jul
 2018 16:51:57 +0800
From: =?gb2312?B?1uzmug==?= <aaaaaa@a.com.cn>
To: Mitsuhiro Taketani <bbb@a.co.jp>
CC: =?gb2312?B?J7PYucixvrK/6Uy4vbXuJw==?= <cccc@a.co.jp>,
 =?gb2312?B?J8371MIgpN+kwaTrJw==?= <ddd@a.co.jp>,
 =?gb2312?B?xr3M78ypueI=?= <aa@a.com.cn>,
 =?gb2312?B?0e7A2g==?= <aaa@a.com.cn>,
=?gb2312?B?0e7Bq8Gr?=
 <vvv@a.com.cn>, =?gb2312?B?J9PxtKiyv+lMJw==?=
 <aaa@a.co.jp>
Subject:
 
=?gb2312?B?tPC4tDogUmU616q3ojogUmU616q3ojogODYyMsrH1f2ESdbDudzA7caxo6g=?=
 =?gb2312?B?pdml86XJMjY3pa2lutGo2J7NqKOpsGvQ0A==?=
Thread-Topic:
 
=?gb2312?B?UmU616q3ojogUmU616q3ojogODYyMsrH1f2ESdbDudzA7caxo6il2aXzpcky?=
 =?gb2312?B?NjelraW60ajYns2oo6mwa9DQ?=
Thread-Index:
 
AdQRlTBF+96YxTU8TFm2x82YWyu5rAAQloew//+QQgD//3Z70IAApx2A//6JlcCAAomJAP//av/Q
//z/lOD/+fzAkP/z9DSg

其同一账号在使用exchange模式收邮件时无此类空白发件人邮件。

这是什么原因导致的呢？查看日志并无什么异常啊。