【メールサーバ】メール利用のポート開放

ポート開放
ルーターの設定で25番ポート(SMTP用)と
110番ポート(POP用)または143番ポート(IMAP用)を開放し、
iptablesでも上記ポートを開放します。

iptables -L --line-numbers

Chain INPUT (policy ACCEPT)
num  target     prot opt source    destination
1    ACCEPT     all  --  anywhere  anywhere     state RELATED,ESTABLISHED
2    ACCEPT     icmp --  anywhere  anywhere
3    ACCEPT     tcp  --  anywhere  anywhere     state NEW tcp dpt:ssh
4    ACCEPT     tcp  --  anywhere  anywhere     tcp dpt:http
5    ACCEPT     tcp  --  anywhere  anywhere     tcp dpt:https
6    REJECT     all  --  anywhere  anywhere     reject-with icmp-host-prohibited

5番目と6番目の間にメール用のポートを設定します。

iptables -I INPUT 6 -p tcp -m tcp --dport 25 -j ACCEPT
iptables -I INPUT 7 -p tcp -m tcp --dport 110 -j ACCEPT
service iptables save

iptables -L --line-numbers

Chain INPUT (policy ACCEPT)
num  target     prot opt source    destination
1    ACCEPT     all  --  anywhere  anywhere     state RELATED,ESTABLISHED
2    ACCEPT     icmp --  anywhere  anywhere
3    ACCEPT     tcp  --  anywhere  anywhere     state NEW tcp dpt:ssh
4    ACCEPT     tcp  --  anywhere  anywhere     tcp dpt:http
5    ACCEPT     tcp  --  anywhere  anywhere     tcp dpt:https
6    ACCEPT     tcp  --  anywhere  anywhere     tcp dpt:smtp
7    ACCEPT     tcp  --  anywhere  anywhere     tcp dpt:pop3
8    REJECT     all  --  anywhere  anywhere     reject-with icmp-host-prohibited

下記サイトでポートの開放を確認します。
http://www.cman.jp/network/support/port.html