配置postfix能自由转发内网的邮件： 就改一个地方即可
vi /etc/postfix/main.cf
...
mynetworks = 127.0.0.0/8, 172.16.0.0/16
...
配置个黑洞，所有邮件都受到，然后drop掉
relayhost =
relay_transport = relay
relay_domains = static:ALL
smtpd_end_of_data_restrictions = check_client_access static:discard
当然，也可以把这些邮件都给送到amavis去，训练找出垃圾邮件
测试邮件发送的命令：
echo "body of your email" | mail -s "This is a Subject os version" -r "abc@kindlefan.xin" test@abc.com
注意：CentOS和Ubuntu居然都没有mail这条命令的话
yum install mailx
apt-get install bsd-mailx