Enhanced Mail System Status Codes

Email Hack
Image by Ross Mayfield via Flickr

用低成本的办法建设一个稳健的,高效的邮件系统应该是每个系统管理员的梦想。现实中太多企业的 IT 人员喜欢采用商业的解决方案了。 在调试反垃圾系统的过程中,再次温习 dsn(delivery status notifications) 的含义。

   Status codes thus consist of three numerical fields separated by ".".
   The first sub-field indicates whether the delivery attempt was
   successful (2= success, 4 = persistent temporary failure, 5 =
   permanent failure).  The second sub-field indicates the probable
   source of any delivery anomalies, and the third sub-field denotes a
   precise error condition, if known.

对系统管理员,需要检查 dsn 不等于 2.0.0 的邮件,来保证邮件系统没有被滥用。例如:

May 18 20:50:30 freelamp sendmail[6221]: n4ICmNJA006201: to=username@21cn.com, delay=00:01:59, xdelay=00:01:44, mailer=esmtp, pri=
181763, relay=mta.21cn.com. [], dsn=4.0.0, stat=Deferred: Connection reset by mta.21cn.com.
May 18 21:24:16 freelamp sendmail[10978]: n4ICmNJA006201: to=user@21cn.com, delay=00:35:45, xdelay=00:00:03, mailer=esmtp, pri
=271763, relay=mta.21cn.com. [], dsn=5.0.0, stat=Service unavailable
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