我设置了 Linux 防火墙，但当激活“丢弃所有内容”规则时，它无法让我的电子邮件客户端连接到服务器。我还更改了规则的顺序，但没有效果。以下是配置：
iptables -L
Chain INPUT (policy ACCEPT)
target prot opt source destination
ACCEPT tcp -- anywhere anywhere tcp dpt:webmin
ACCEPT tcp -- anywhere anywhere tcp dpt:imaps
ACCEPT tcp -- anywhere anywhere tcp dpt:submission
ACCEPT tcp -- anywhere anywhere tcp dpt:urd
ACCEPT tcp -- anywhere anywhere tcp dpt:https
ACCEPT tcp -- anywhere anywhere tcp dpt:imap2
ACCEPT tcp -- anywhere anywhere tcp dpt:http
ACCEPT udp -- anywhere anywhere udp dpt:domain
ACCEPT tcp -- anywhere anywhere tcp dpt:domain
ACCEPT tcp -- anywhere anywhere tcp dpt:smtp
ACCEPT tcp -- anywhere anywhere tcp dpt:ssh
ACCEPT tcp -- anywhere anywhere tcp dpt:ftp
DROP all -- anywhere anywhere
你知道这是什么原因吗？