诈骗邮件仿造了我们的邮件地址，能够发给好多人邮件，不清楚为什么？

邮件头如下

Received: from pD958FE44.dip0.t-ipconnect.de ([217.88.254.68])
          by mail.sieyuan.com (Lotus Domino Release 8.5.3FP6)
          with ESMTP id 2018112422334365-70825 ;
          Sat, 24 Nov 2018 22:33:43 +0800 
Date: 24 Nov 2018 15:28:07 +0000
From: <0xljd7dcb2bfb4f3c2a5z.syec@sieyuan.com>
X-Priority: 3 (Normal)
Message-ID: <723331263.201811241533@sieyuan.com>
To: <0xljd7dcb2bfb4f3c2a5z.syec@sieyuan.com>
Subject: Security Warning. Third party accessed to 
0xljd7dcb2bfb4f3c2a5z.syec@sieyuan.com.
MIME-Version: 1.0
X-MIMETrack: Itemize by SMTP Server on sycloud/siyuan(Release 
8.5.3FP6|November 21, 2013) at
 2018/11/24 22:33:44,
         
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近期收到一封诈骗邮件，收件人地址为：×××@我们公司域名，好多人收到了这封邮件。后面再发该地址，还是好多人能够收到。
所以不清楚该地址：0xljd7dcb2bfb4f3c2a5z.syec@sieyuan.com 怎么回事，我们通讯录中也没有该地址。