Postfix什么时候使用IPv6？什么时候使用IPv4？

我已经为IPv6和IPv4配置了我的邮件服务器，但是在大多数情况下，它使用IPv4，而远程主机上可以使用IPv6。我在2.9版中使用Postfix。所以我的想法是，如果可用，postfix将使用IPv6并回退到IPv4，还是我错了？

您是否已将smtp_address_preference选项设置为显示优先IPv6？

从postconf（5）：

smtp_address_preference (default: any)
       The address type ("ipv6", "ipv4" or "any") that the Postfix SMTP client will try first, when a destination has IPv6 and IPv4 addresses with equal MX preference. This feature has no effect unless  the
       inet_protocols setting enables both IPv4 and IPv6.  With Postfix 2.8 the default is "ipv6".

       Notes for mail delivery between sites that have both IPv4 and IPv6 connectivity:

       ·      The setting "smtp_address_preference = ipv6" is unsafe.  It can fail to deliver mail when there is an outage that affects IPv6, while the destination is still reachable over IPv4.

       ·      The setting "smtp_address_preference = any" is safe. With this, mail will eventually be delivered even if there is an outage that affects IPv6 or IPv4, as long as it does not affect both.

       This feature is available in Postfix 2.8 and later.

授予Postfix正确配置了IPv6的权限后，它被指示使用两种协议，并且所连接的MX主机同时具有A和AAAA记录，Postfix每次都会随机选择一次，正如Wietse Wenema自己解释的那样：

最近的Postfix SMTP客户端在IPv4和IPv6之间随机选择，以便当两者之一关闭时邮件不会卡住。