MX record and MX record priority

MX record and MX record priority
MX mx (Mail exchanger) record
is a mail exchange record that points to a mail server that is used to locate a mail server based on the recipient's address suffix when the e-mail system sends a message. For example, when a user on the internet wants to send a letter to user@mydomain.com, the user's mail system finds an MX record of the domain name mydomain.com through DNS, and if the MX record exists, The user's computer sends the message to the mail server specified by the MX record.
Ways to check if MX records exist
A very useful tool for DNS queries is nslookup, which you can use to query the various data in DNS. You can run Nslookup directly under Windows command line into an interactive mode where you can query for various types of DNS data.
DNS name resolution data can be of various types, with the SOA type data setting this zone parameter, with the type a data for the IP address that sets the name, and the MX type data that sets the mail exchange. These different types of data can be queried through the Nslookup interactive mode, and the set type command can be used to set the corresponding query type during the query.
Such as:
C:/Documents and Settings/administrator>nslookup
Default server:a.center-dns.jsinfo.net
address:218.2.135.1

> Set TYPE=MX
> sohu.com
Server:a.center-dns.jsinfo.net
address:218.2.135.1

 non-authoritative Answer:
 sohu.com        MX preference = 5, Mail exchanger = sohumx1.sohu.com
 sohu.com        MX preference = ten, mail Exchanger = sohumx.h.a.sohu.com

sohu.com nameserver = ns2.sohu.com
sohu.com nameserver = ns1.sohu.com
sohu.com nameserver = dns.sohu.com
sohumx1.sohu.com Internet address = 220.181.26.202
ns2.sohu.com Internet address = 220.181.26.167
dns.sohu.com Internet address = 61.135.150.76
ns1.sohu.com Internet address = 61.135.179.169
If the MX record for a domain name you are looking for does not exist, a hint similar to the following appears:
> 71mc.net
Server:a.center-dns.jsinfo.net
address:218.2.135.1

A.center-dns.jsinfo.net can ' t find 71mc.net:non-existent domain
You can also use commands such as NSLOOLUP-QT=MX 71mc.net to query 71mc.net MX records

MX precedence is meaningless when there is only one MX record.

The smaller the value of the

mx  number, the higher the priority. The same domain name has two different priority MX records, usually with a high priority. When a high priority machine is not available, a low priority can play a temporary backup function, collecting mail and forwarding. When high priority machines are normal, low-level attempts to forward the letters to the higher-priority servers.