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邮件交换记录，它指向一个邮件服务器，用于电子邮件系统发邮件时根据收信人的地址后缀来定位邮件服务器。
MX记录也叫做邮件路由记录，用户可以将该域名下的邮件服务器指向到自己的mail server上，然后即可自行操控所有的邮箱设置。

上面的定义有点抽象。

dig 163.com -t mx

;; ANSWER SECTION:
163.com. 9782 IN MX 10 163mx01.mxmail.netease.com.
163.com. 9782 IN MX 10 163mx02.mxmail.netease.com.
163.com. 9782 IN MX 10 163mx03.mxmail.netease.com.
163.com. 9782 IN MX 50 163mx00.mxmail.netease.com.

MX记录也叫做邮件路由记录，用户可以将该域名下的邮件服务器指向到自己的mail server上。
163mx00.mxmail.netease.com 这些究竟是什么？
ping 163mx00.mxmail.netease.com
PING 163mx00.mxmail.netease.com (123.125.50.140) 56(84) bytes of data.
ping 163mx01.mxmail.netease.com
PING 163mx01.mxmail.netease.com (220.181.14.137) 56(84) bytes of data.
ping 163mx02.mxmail.netease.com
PING 163mx02.mxmail.netease.com (220.181.14.146) 56(84) bytes of data.
ping 163mx03.mxmail.netease.com
PING 163mx03.mxmail.netease.com (220.181.14.160) 56(84) bytes of data.

1。163mx00.mxmail.netease.com 这些是邮件路由服务器？

2。dig 163.com -t mail
;; ANSWER SECTION:
163.com. 300 IN A 123.58.180.7
163.com. 300 IN A 123.58.180.8

123.58.180.7 123.58.180.8 是邮件服务器吗？

ping mail.163.com
PING mail163.ntes53.netease.com (123.125.50.28) 56(84) bytes of data.
ping smtp.163.com
PING smtp.163.com (123.125.50.133) 56(84) bytes of data.
ping pop3.163.com
PING pop3.163.idns.yeah.net (123.125.50.29) 56(84) bytes of data.
ping imap.163.com
PING imap.163.com (123.125.50.47) 56(84) bytes of data.

为何两者对不上？

參閱

1. https://help.ubuntu.com/16.04/servergui ... cord-types
Common Record Types
MX record: Used to define where email should be sent to. Must point to an A record, not a CNAME.
IN MX 1 mail.example.com.
mail IN A 192.168.1.13

dig 163.com -t mail
;; ANSWER SECTION:
163.com. 300 IN A 123.58.180.7
163.com. 300 IN A 123.58.180.8

123.58.180.7 123.58.180.8 是邮件服务器吗？

2. https://help.ubuntu.com/16.04/servergui ... cord-types
Common Record Types
A record: This record maps an IP Address to a hostname.
www IN A 192.168.1.12

ping mail.163.com
PING mail163.ntes53.netease.com (123.125.50.28) 56(84) bytes of data.
...
为何两者对不上？

3. 實做一次
ping mail.163.com
PING mail163.ntes53.netease.com (54.215.2.217) 56(84) bytes of data.
顯然 mail.163.com 對應的 IP 並非唯一 猜測 伺服器 不只一個