From: Mail Delivery System [mailto:MAILER-DAEMON@mail.krisun.com]
Sent: Wednesday, July 20, 2011 6:50 PM
To: jane
Subject: DELIVERY FAILURE: 553 5.3.0 flpd112 DNSBL:ATTRBL 521<
220.231.134.75 >_is_blocked.__For_information_see_http://att.net/blocks
This is the mail system at host mail.krisun.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 mail system
<jwanger@pacbell.net>: host pbimail4.prodigy.net[207.115.21.21] said: 553 5.3.0
    flpd112 DNSBL:ATTRBL 521< 220.231.134.75
    >_is_blocked.__For_information_see_http://att.net/blocks (in reply to MAIL
    FROM command)
 
解决方法：
   1.测试DNS解析正常。
   2. 登录http://att.net/blocks 更加对应的错误信息，登录到http://www.att.net/general-info/521.html 进行解封就可以了。