1.安装postfix-policyd的时候会提示mysql连接失败，因为使用了空密码。iredmail.sh会退出
这时候使用 aptitude 或者 apt-get 安装postfix-policyd，会出现数据库配置对话框，输入密码即可正常安装

2.我当时因为安装不成功，所以卸载了相关软件想重新安装，结果到了 amavisd-new 又失败
提示

    Creating/updating amavis user account...
    Broken amavis system user found.  To insure data-safety,
    it is up to you the local administrator to remove the broken
    amavis user, or repair it so that it is sane
    dpkg: error processing amavisd-new (--configure):
     subprocess post-installation script returned error exit status 1
    Errors were encountered while processing:
     amavisd-new

原因是 amavisd-new 会创建 amavis 和 amavis组，但卸载的脚本有bug没有删除amavis用户。
userdel amavis 删除 amavis用户
再继续安装即可