Make the spam of Dynamic IP users nowhere invisible

As the access cost decreases, more and more spammers in China use dynamic address dial-in to send spam. This method can both reduce the cost and avoid blocking and tracing. For such dynamic IP addresses, it is often difficult for mail service providers to make judgments. However, at present, 263 emails can be used to make the spam of Dynamic IP users invisible. How is this judgment made? What new technology is it?

In fact, there are two roles in the mail system for sending mail. One is to receive the users of the system (
 
 
A mail sent by a service provider) is used to deliver the corresponding mail to another mail server or the mailbox of the user on this server, which is called the SMTP server; the other is responsible for receiving mails from other email servers delivered to the users on this server, called the MX Server. This group of servers only receive emails from users in the system.

In this way, emails sent to and from users in the same system can only pass through the SMTP server group, instead of the MX Server group. In general, the IP addresses connected to the MX Server are the IP addresses of the mail server and are not directly facing users. In this way, most dynamic IP addresses cannot be used as mail servers. Therefore, requests from these IP addresses and connections to the MX Server are more likely to be spam. Therefore, you only need to list these IP addresses in the form of 'real-time blacklist' (RBL, shared among multiple MX servers, so that we can effectively reject this part of spam.