Today, the proliferation of spam, junk mail to our lives, work, learn to bring great harm. Transmitting the lack of effective authentication mechanism between the SMTP server, even if the technical effect of blocking spam detection is still general, addition block spam detection technology is mainly identified after receiving a letter according to certain conditions and requires a large amount of server resources If it can take certain means before the letter arrives at the server, so that we can greatly improve the efficiency of the server. Consequently, many mail servers such as sina.com, hotmail.com, yahoo.com.cn etc. are used to block spam identification technology + IP reverse DNS verification technology to block spam better.
Let's take a look at what is the IP reverse analysis. In fact, a friend made the DNS server DNS server will know that there are two areas, namely, "Forward Lookup Zones" and "Reverse Lookup Zones", the reverse lookup zone that is the reverse resolve the IP mentioned here, it's role is to get the IP address of the domain name pointed to by PTR record query IP addresses, of course, would be needed to successfully get the domain name has PTR record for the IP address.
So how IP reverse analysis is applied to the mail server to block spam it? Let's look at an example:
One day, Ah Q to the A's visit, he handed him a business card, business card says he is from information "underworld murder club" as well as telephone numbers, A company that should be a brief survey of the history of Ah Q, then hit phone to the phone number on the business card of Ah Q belongs to the bureau were verified, the bureau told the a's if their phone number is not a "gangster murder club", then a will reject the call of Ah Q, if their phone number really belongs to "underworld murder club ", a company may accept the call of Ah Q may also be further verified, so he called the" underworld murder club "belongs registry query, if the answer to confirm that the club does have this telephone number, company a will accept Ah Q's visit, otherwise will refuse to visit Ah Q.
In this example, Ah Q is like our mail server, A is the other mail server, "underworld murder club" is the HELO domain of our mail server server to communicate with each other messages used (not a mail domain name after the @ address), phone number on the card is the export of our mail server public IP address. Process A company investigation of Ah Q is equivalent to a reverse DNS verification process. This shows that the reverse is actually the other server parsing validation in progress, if we do not reverse analysis, then the other server's reverse lookup validation will fail, so will the other server is unknown to us and refused to sender we receive messages sent to, which is after we excluded other causes (such as the other side was included in the blacklist, no MX record, using a dynamic IP address, etc.) can not be to sina.com when did not do the reverse analysis, the reason homail.com the letter.
So how well do we should reverse lookup? First of all have a fixed public IP addresses, domain names available (best not to be used by the other services), for example, you have diyway.net domain name, you can ask your domain registrar to add a domain name for you and mx.diyway.net a record to point to your SMTP server exports a public IP address, such as: 61.192.56.23, then please contact your fixed IP belongs ISP (general Telecom or Netcom) required for your IP reverse analysis to mx.diyway. net. After completing the HELO domain name of your SMTP server Do not forget to change mx.diyway.net, so that they can achieve their goals.
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nslookup –qt=ptr yourIP
For example, my domain is diyway.net
my mail server address is: mail.diyway.net
mailbox user name format for the [email protected]
set up a mail system on the mail server HELO is: mx.diyway.net
mail server for the IP : 61.192.56.23
find a local telecommunications do this 61.192.56.23 IP anti-analytic to mx.diyway.net
On Windows systems, enter cmd in the Run command enter nslookup -qt in the open window = ptr 61.192.56.23
Return information is as follows:
C: \ Documents and Settings \ the User> nslookup ptr = -QT 61.192.56.23
Server: mx.diyway.net
Address: 61.192.56.23
Note Reverse resolve this IP is a success.
返回信息如下
C:\Documents and Settings\user>nslookup –qt=ptr 61.192.56.23
*** Can't find server name for address 61.142.80.154: Non-existent domain
Server: UnKnown
Address: 61.192.56.23
Note Reverse resolve the IP does not work.
Reproduced in: https: //www.cnblogs.com/Spring/archive/2007/05/16/748951.html