情况：
登录服务器后，控制台会不断提示以下错误：
SYSERR(root): savemail: cannot save rejected email
/var/tmp/dead.letter 增长迅速
日志：
From MAILER-DAEMON Mon Mar 1 11:57:40 2010
Return-Path: <MAILER-DAEMON>
Received: from localhost (localhost)
by hwcln43.ebis.com (8.9.3/8.9.3) with internal id L~X06469;
Mon, 1 Mar 2010 11:57:40 +0800 (EAT)
Date: Mon, 1 Mar 2010 11:57:40 +0800 (EAT)
From: Mail Delivery Subsystem <MAILER-DAEMON>
Message-Id: <201003010357.L~X06469@hwcln43.ebis.com>
To: root
MIME-Version: 1.0
Content-Type: multipart/report; report-type=delivery-status;
boundary="L~X06469.1267415860/hwcln43.ebis.com"
Subject: Returned mail: Host unknown (Name server: wcat: host not found)
Auto-Submitted: auto-generated (failure)
分析：
系统发错误邮件到本地账户时，发给了 username@wcat
sendmail.cf 的 [DR] 设置为 [DR wcat] ，配置错误
处理方法：
1.把 /etc/mail/sendmail.cf 的 [DR wcat] 改为 [DR]
2./sbin/init.d/sendmail stop
3./sbin/init.d/sendmail start
