Basic concepts for domain names, DNS, A records, and MX records

For any valid domain name, there should be an authoritative domain name server (DNS) for that domain, and one or more resource records for that domain name in the domain name server.
There are 5 items in a resource record, namely, domain name (domain_name), Lifetime (time_to_live), type (type), Class (Class), and value.

which
Domain name: Is the domain that this record points to;
Time to live: Indicates the stability of the record. Highly stable information is given a large value, such as 86 400 (the number of seconds in a day), and a large change of information is given to a smaller value, such as 60 (1 minutes);
Type: Indicates the type of record in which the important types are:

type	meaning	value
soa	start of authority	the parameters of the zone
a host IP address	32 bit integer
mx	Mail exchange	ns

One of the most common records is a record, which resolves the server in the home page of the domain name through a record. In addition to a record, if there is a mail service with the domain name as the mailing address, you must have an MX record to resolve the mail server for that domain name through the MX record. such as: abc.com.cn 86400 in MX 1 mx.sina.net