What is MX (Mail exchanger?

MX is called a mail exchange record.

Most netizens will have one or more free mailboxes, using Gmail, Hotmail, QQ, 163, etc.
Our mailbox address format is: userName@gmail.com, userName@hotmail.com, userName@qq.com, userName@163.com

When your friends use the mailbox friend@qq.com to send an email to your mailbox userName@gmail.com
1.1 your friend's email system is mail.qq.com
1.2 mail.qq.com Q: userName@gmail.com what is your domain name, my home is QQ.com
1.3 userName@gmail.com answer: Of course it is gmail.com you won't look at @?
1.4 mail.qq.com: What email system are you using?
1.5 gmail.com A: My boss bought the domain name www.gmail.com and added mail.gmail.com to the above MX record. What do you mean I use?
1.6 Oh, mail.gmail.com.

The MX record can be modified on the DNS of the domain name to indicate who provided the mail service.
It usually takes 2-24 hours for an MX record to take effect. The modification and addition of domain name resolution are only modified on the DNS of the domain name provider, the DNS server used by others may not be the same as the DNS server on which you apply for domain name resolution. Therefore, when your domain name is added or modified, the correct resolution result can only be seen after data synchronization between DNS servers, so the domain name resolution cannot take effect immediately after the change.

Similar to using enterprise mail userName@company.com
Your friend friend@qq.com sends an email to the userName@company.com, which is also the first to resolve the MX record of company.com, you can change the MX record of your domain name, choose provided by mail.qq.com or mail.gmail.com, the default is generally mail.company.com. Of course, you must first apply to QQ or Gmail for providing this email service for your domain name.

----------------------------------------- how can I conveniently view the MX record modification and take effect?
RUN CMD
NSLookup (DNS lookup)
set q = Mx (MX record viewing)
company.com (detailed information is returned ...)