客户无法收信

ec40

各位大虾：
       最近遇到一个问题，客户反应说与外面公司通信时，无法收到对方的来信（带附件100%收不到，不带附件偶尔可以收到），对方将发信的报错信息反馈如下：
This is the Postfix program at host smtp1.263xmail.com.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to <postmaster>

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

The Postfix program

<xiang.wang@XXX.com>: lost connection with
    mx2.XXX.com while sending message body