我的 iptables 规则：
# delete all current rules and user chains
iptables -F
iptables -X
# global policy (target by default)
iptables -P INPUT DROP
iptables -P OUTPUT DROP
iptables -P FORWARD DROP
# localhost
iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT
# dns -> udp
iptables -A INPUT -i eth0 -p udp --sport 53 -m state --state ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p udp --dport 53 -m state --state NEW,ESTABLISHED -j ACCEPT
# http
iptables -A INPUT -i eth0 -p tcp --dport 80 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 80 -m state --state ESTABLISHED -j ACCEPT
# ssh
iptables -A INPUT -i eth0 -p tcp --dport 29415 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 29415 -m state --state ESTABLISHED -j ACCEPT
# final LOG
iptables -A INPUT -i eth0 -m limit -j LOG --log-prefix "[fortress:unrule_input] "
iptables -A OUTPUT -o eth0 -m limit -j LOG --log-prefix "[fortress:unrule_output] "
# --log-ip-options --log-tcp-options
# final DROP
iptables -A INPUT -i eth0 -j DROP
iptables -A OUTPUT -o eth0 -j DROP
端口 25 未打开。默认策略为 DROP。
只有通过 udp 协议才可以从服务器发送新数据包并建立连接。
但 Postfix 仍会发送邮件...
为了进行测试，我在命令行中使用了这个：
php -a
mail('[email protected]', 'subject', 'body');
输出iptables -vL
Chain INPUT (policy DROP 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
48089 1119M ACCEPT all -- lo any anywhere anywhere
1518 165K ACCEPT udp -- eth0 any anywhere anywhere udp spt:domain state ESTABLISHED
86211 5672K ACCEPT tcp -- eth0 any anywhere anywhere tcp dpt:http state NEW,ESTABLISHED
2498 184K ACCEPT tcp -- eth0 any anywhere anywhere tcp dpt:29415 state NEW,ESTABLISHED
18 840 LOG all -- eth0 any anywhere anywhere limit: avg 3/hour burst 5 LOG level warning prefix "[fortress:unrule_input] "
1430 75592 DROP all -- eth0 any anywhere anywhere
Chain FORWARD (policy DROP 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
Chain OUTPUT (policy DROP 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
48089 1119M ACCEPT all -- any lo anywhere anywhere
1524 112K ACCEPT udp -- any eth0 anywhere anywhere udp dpt:domain state NEW,ESTABLISHED
181K 253M ACCEPT tcp -- any eth0 anywhere anywhere tcp spt:http state ESTABLISHED
1781 627K ACCEPT tcp -- any eth0 anywhere anywhere tcp spt:29415 state ESTABLISHED
18 948 LOG all -- any eth0 anywhere anywhere limit: avg 3/hour burst 5 LOG level warning prefix "[fortress:unrule_output] "
346 20488 DROP all -- any eth0 anywhere anywhere
/var/log/邮件日志
May 21 14:50:44 CentOS-70-64-minimal postfix/qmgr[5169]: B79F311800AB: removed
May 21 14:50:44 CentOS-70-64-minimal postfix/smtp[5484]: B79F311800AB: to=<[email protected]>, relay=mx.domen.tl[2a02:6b8::89]:25, delay=121, delays=0.14/0.01/120/0.85, dsn=2.0.0, status=sent (250 2.0.0 Ok: queued on mxfront10j.mail.yandex.net as 1432212643-e6gErcsB7d-ohqGfFN0)
May 21 14:50:42 CentOS-70-64-minimal postfix/smtp[5484]: connect to mx.domen.tl[213.180.204.89]:25: Connection timed out
May 21 14:50:12 CentOS-70-64-minimal postfix/smtp[5484]: connect to mx.domen.tl[93.158.134.89]:25: Connection timed out
May 21 14:49:42 CentOS-70-64-minimal postfix/smtp[5484]: connect to mx.domen.tl[213.180.193.89]:25: Connection timed out
May 21 14:49:12 CentOS-70-64-minimal postfix/smtp[5484]: connect to mx.domen.tl[77.88.21.89]:25: Connection timed out
May 21 14:48:43 CentOS-70-64-minimal postfix/qmgr[5169]: CA04D11800A6: removed
May 21 14:48:43 CentOS-70-64-minimal postfix/smtp[5485]: CA04D11800A6: to=<[email protected]>, orig_to=<[email protected]>, relay=gmail-smtp-in.l.google.com[2a00:1450:4013:c01::1b]:25, delay=0.27, delays=0.08/0.01/0.1/0.09, dsn=2.0.0, status=sent (250 2.0.0 OK 1432212522 t8si3023064wjr.69 - gsmtp)
May 21 14:48:42 CentOS-70-64-minimal postfix/local[5483]: B79F311800AB: to=<[email protected]>, relay=local, delay=0.23, delays=0.14/0.01/0/0.08, dsn=2.0.0, status=sent (forwarded as CA04D11800A6)
May 21 14:48:42 CentOS-70-64-minimal postfix/qmgr[5169]: CA04D11800A6: from=<[email protected]>, size=571, nrcpt=1 (queue active)
May 21 14:48:42 CentOS-70-64-minimal postfix/cleanup[5481]: CA04D11800A6: message-id=<[email protected]>
May 21 14:48:42 CentOS-70-64-minimal postfix/qmgr[5169]: B79F311800AB: from=<[email protected]>, size=403, nrcpt=2 (queue active)
May 21 14:48:42 CentOS-70-64-minimal postfix/cleanup[5481]: B79F311800AB: message-id=<[email protected]>
May 21 14:48:42 CentOS-70-64-minimal postfix/pickup[5376]: B79F311800AB: uid=0 from=<root>
猫规则
# Generated by iptables-save v1.4.21 on Thu May 21 15:18:19 2015
*filter
:INPUT DROP [0:0]
:FORWARD DROP [0:0]
:OUTPUT DROP [0:0]
-A INPUT -i lo -j ACCEPT
-A INPUT -i eth0 -p udp -m udp --sport 53 -m state --state ESTABLISHED -j ACCEPT
-A INPUT -i eth0 -p tcp -m tcp --dport 80 -m state --state NEW,ESTABLISHED -j ACCEPT
-A INPUT -i eth0 -p tcp -m tcp --dport 29415 -m state --state NEW,ESTABLISHED -j ACCEPT
-A INPUT -i eth0 -m limit --limit 3/hour -j LOG --log-prefix "[fortress:unrule_input] "
-A INPUT -i eth0 -j DROP
-A OUTPUT -o lo -j ACCEPT
-A OUTPUT -o eth0 -p udp -m udp --dport 53 -m state --state NEW,ESTABLISHED -j ACCEPT
-A OUTPUT -o eth0 -p tcp -m tcp --sport 80 -m state --state ESTABLISHED -j ACCEPT
-A OUTPUT -o eth0 -p tcp -m tcp --sport 29415 -m state --state ESTABLISHED -j ACCEPT
-A OUTPUT -o eth0 -m limit --limit 3/hour -j LOG --log-prefix "[fortress:unrule_output] "
-A OUTPUT -o eth0 -j DROP
COMMIT
# Completed on Thu May 21 15:18:19 2015
答案1
您的iptables规则正在执行您想要的操作：它们正在阻止出站端口 25 连接：
May 21 14:50:12 CentOS-70-64-minimal postfix/smtp[5484]: connect to mx.domen.tl[93.158.134.89]:25: Connection timed out
不幸的是，你的服务器似乎也有一个有效的 ipv6 地址（我猜它是一个现代的 VPS，我注意到现在大多数 VPS 都启用了 v6），而且现在很多提供商都宣传 v6 邮件服务器，所以向这些服务器投递邮件很顺利：
May 21 14:48:43 CentOS-70-64-minimal postfix/smtp[5485]: CA04D11800A6: to=<[email protected]>, orig_to=<[email protected]>, relay=gmail-smtp-in.l.google.com[2a00:1450:4013:c01::1b]:25, delay=0.27, delays=0.08/0.01/0.1/0.09, dsn=2.0.0, status=sent (250 2.0.0 OK 1432212522 t8si3023064wjr.69 - gsmtp)
请注意地址：2a00:1450:4013:c01::1b，这不是 v4 地址。您需要确保您的 ipv6 规则还你想多严格就多严格ip6tables -L -n -v。欢迎来到 21 世纪！
编辑：我无法告诉你ip6tables应该拥有哪些规则，但语法大致相同，是的。你可以选择复制或不复制你的规则集，但你留下了一个大的如果您没有同样精心设计的 IPv6 规则，那么您的安全性就会存在漏洞。