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一台测试用的邮件服务器 ContOS6.6，修改 /etc/modprobe.d/dist.conf 添加以下两行内容以禁用 IPv6, 然后重启
166 alias net-pf-10 off
167 alias ipv6 off
重启完之后发现 dovecot 服务启不来了，查看 boot.log 发现还有 ip6tables 也没有启用，这个好说，禁用 IPv6 了 IPv6 的防火墙也不需要了，chkconfig ip6tables off 就行了。
在 boot.log 中看到 dovecot 相关的错误日志如下：
Dovecot Imap：Error: socket() failed: Address family not supported by protocol
Error: service(managesieve-login): listen([::], 4190) failed: Address family not supported by protocol
Error: socket() failed: Address family not supported by protocol
Error: service(pop3-login): listen([::], 110) failed: Address family not supported by protocol
Error: socket() failed: Address family not supported by protocol
Error: service(pop3-login): listen([::], 995) failed: Address family not supported by protocol
Error: socket() failed: Address family not supported by protocol
Error: service(lmtp): listen([::], 24) failed: Address family not supported by protocol
Error: socket() failed: Address family not supported by protocol
Error: service(imap-login): listen([::], 143) failed: Address family not supported by protocol
Error: socket() failed: Address family not supported by protocol
Error: service(imap-login): listen([::], 993) failed: Address family not supported by protocol
Fatal: Failed to start listeners [失败]
根据错误提示，是 IPv6 相关的协议启不来，那么就去修改 dovecot 的配置文件 /etc/dovecot/devecot.conf
vi 打开文件后在文件是搜索 listen 和 [::]，其实也不用搜了，就是第六行了
先注释掉 listen = * [::]
然后再插入一行 listen = *
:wq 保存
service dovecot start 启动服务，OK
