今天在安装 Virtualmin for Webmin 时碰到一个问题：启用 Postfix 时出错，出错信息为：
A problem was found with your Postfix virtual maps : No map sources were found in the Postfix configuration
解决方法是： edit the /etc/postfix/main.cf file and add:
virtual_alias_maps = hash:/etc/postfix/virtual