The steps of IP reverse resolution (PTR record) analysis _win server

Source: Internet
Author: User
Spam in the flood of today, spam to our lives, work, learning has brought great harm. Because of the lack of effective authentication mechanism between SMTP servers, even if the use of spam identification blocking technology is still common, and the spam identification and blocking technology is mainly in the receipt of letters according to a certain condition to identify, the need to consume a large number of server resources, if the letter to the server before the adoption of a , this will greatly improve the efficiency of the server. Therefore, many mail servers such as,, and so on have adopted the spam identification blocking technology +IP reverse resolution verification technology to better block spam.
Let's take a look at what IP reverse parsing is. In fact, a friend who has been a DNS server must know that there are two zones in the DNS server, that is, "forward lookup zone" and "Reverse lookup zone", reverse lookup zone that is the IP reverse resolution, which is the role of the IP address by querying the PTR record to get the IP address to the domain name, of course, A PTR record of the IP address is required to successfully get the domain name.
So how is IP reverse parsing applied to the mail server to block spam? Let's take a look at one of the following examples:
One day, ah Q to a company visit, he handed a business card, the card said he came from the "Mafia Homicide Club" and telephone numbers and other information, a company that should be the origin of AH Q to do a simple investigation, so call a Q business card on the telephone number of the Telecommunications Bureau to verify, If the Telecommunications Bureau tells company A that its phone number does not belong to the Mafia Homicide Club, then a company will reject the visit of Ah Q, if its phone number does belong to the "Mafia Homicide Club", a company may accept a visit may also be further verified, so he called the "mafia Homicide Club," the registration agency to inquire, If the answer confirms that the club does have the phone number, a company will accept a visit from Ah Q, or it will refuse to visit.
In this example, ah Q is like our mail server, a company is the other mail server, "Mafia Homicide Club" is our mail server and the other mail server to use the HELO domain name (not the domain name after the email address), The telephone number on the business card is the public network IP address of our mail server export. The process of a company's investigation of AH Q is equivalent to a reverse parsing verification process. This shows that the reverse parsing verification is actually the other server in progress, if we do not do reverse parsing, then the opposite side of the server's reverse resolution verification will fail, so that the other server will be we are unknown to the sender to reject the mail we send, which is that we exclude other reasons (such as by the other side blacklisted, No MX records, use of dynamic IP addresses, and so on) The reason why you cannot send and when you do not have a reverse parsing.

So how do we do the reverse analysis smoothly? The first is to have a fixed public network IP address, the available domain name (preferably not to be used by other services), For example, if you have a domain name, you can ask your domain registrar to add a domain name to you and point a record to your SMTP server export public IP address, such as:, and then contact your fixed IP-owned ISP Contact request for your IP reverse resolution to When you're done, don't forget to change the HELO domain name of your SMTP server to so you can achieve your goal.
1, do a good reverse analysis of the letter sent to may be transferred to the "Unknown Mail folder", please contact with, ask for you to solve the problem.
2, to see if the reverse resolution is successful, you can use the following command: Nslookup–qt=ptr Yourip, from the returned information you will see the results of the reverse parsing.
3, must have fixed public network IP address and the real domain name available. Also pay attention to the reverse resolution of the domain name a record must point to the ip!
4, for a number of fixed public network IP address, as long as the main export IP reverse analysis can be, no matter how many SMTP servers you have, as long as the IP connection to the extranet will be the HELO domain name of these SMTP servers changed to IP reverse domain name. (is independent of the address domains on these SMTP servers)
5, the presence of domain names and IP addresses are virtual information, if the real people caused inconvenience, please tell, but I do not bear any legal responsibility. +

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