What are secondary domain names, URL forwarding, MX records, and wildcard domain name resolution?

What is a subdomain name, URL forwarding, MX record, wildcard domain name resolution, and what is a subdomain name?
A subdomain name is a relative concept and relative to a parent domain name. Domain names have many levels, separated by vertices. For example, if a company's top-level domain name ends with COM, all domain names ending with COM are its subdomains. For example, www.amaxit.net is the subdomain of amaxit.net, while amaxit.net is the subdomain of net.

What is URL forwarding?
The URL forwarding function is a value-added service provided by our company after domain name registration. URL Forwarding is a special setting of the server that directs the user accessing your current domain name to another network address you specified. For example, URL forwarding allows users to automatically turn to access the http://www.abc.com when accessing the http://www.mydomain.com...

What is an MX record?
Used by the email system to locate the email server based on the recipient's address suffix when sending an email. For example, when the recipient is a user@mydomain.com, the system will parse the MX record in DNS for mydomain.com. If an MX record exists, the system forwards the email to the email server corresponding to the MX record based on the MX record priority.

What is wildcard domain name resolution?
For example, if your domain name is abc.com, all the mail.abc.com settings under it are resolved to the same IP address. For example, if the customer sets mail.abc.com, it will automatically resolve it to the same IP address as abc.com, And the displayed page will be the same as abc.com.