邮件乱码问题

接受到从后台发送给用户的邮件,有乱码问题.

1) 邮件标题不管用中,英文, 均显示正常.

2)邮件主体内容不管用中,英文, 均显示乱码. 乱码如下:
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


附邮件PHP文件,都没有改动过. 邮件系统也是昨天刚刚测试成功.)

求老大解决,谢谢.