[Post] email-Domain Name-DNS knowledge

What is a domain name? What makes a domain name?

A domain name is the name used to search for a website on the internet. It is an important identifier on the internet and is equivalent to a host's house number.Each host corresponds to an IP address. Each IP address consists of a series of numbers, such as 101.25.11.34. People use it for convenience of memoryDomain name in place of these numbers to find the host, such as mydomain.com. Each domain name corresponds to an IP address. people enter the domain name, and then the Domain Name Server (DNS) resolves it into an IP address to find the corresponding website. Domain names are required for each website or EMAIL. An English international domain name can contain up to 67 characters (including suffixes) and can contain English letters, Arabic numerals, and hyphens, each level can contain up to 22 letters. The length of a third-level domain name in China cannot exceed 20 characters. 

What is DNS?

　   Domain Name Management System (DNS)NameSystem) is the domain name resolution server. Its role on the Internet is to convert the domain name into an IP address that can be recognized by the network. For example, when we access the Internet, www.163.com will be automatically converted to 202.108.42.72 

What is A record?
　    A(Address)A record is an IP address record used to specify the Host Name (or domain name. You can direct the website server under this domain name to your webServer. You can also set a second-level domain name for your domain name. 

What is an NS record?

　    NS (NameServer) record is a Domain Name Server record, used to specify the DNS Server to which the domain name is resolved. 

What is an alias record (CNAME )?

　    It is also called a canonical name. This record allows you to map multiple names to the same computer.It is usually used on computers that provide both WWW and MAIL services. For example, there is A computer named "host.mydomain.com" (A record ).It provides WWW and MAIL services at the same time, in order to facilitate user access to the service. You can set two aliases (CNAME) for the computer: WWW and MAIL.The full names of these two aliases are www.mydomain.com and mail.mydomain.com ". In fact, they all point to "host.mydomain.com ". 

What is wildcard domain name resolution?

　    Wildcard domain name resolution is defined:* .A.com under the customer's domain name a.com is resolved to the same IP address.For example, if B .a.com is set, it will automatically resolve it to the same IP address as a.com. 

What is an MX record?

　    Mx (MailExchanger) record is a mail exchange record, which points to a mail server, used by the e-mail system to send mail accordingThe recipient's address suffix to locate the email server. For example, when a user on the Internet wants to send a letterUser@mydomain.comThe user's email system searches for the MX record of the domain name mydomain.com through DNS. If the MX record exists,The user's computer sends the email to the email server specified by the MX record. 

Methods for checking the existence of MX records

　   A very useful tool for DNS query is NSlookup, which can be used to query various data in DNS. You can directly run NSLookup in Windows command line to enter an interactive mode, where you can query various types of DNS data.
 
　   DNS name resolution data can be of different types, including the SOA type data with the parameter set for this zone, and the type data with the IP address corresponding to the parameter set for this zone, there is MX data set for mail exchange. You can use the nslookup interactive mode to query different types of data.SetThe type COMMAND sets the corresponding Query type.
For example:
C:/> nslookup
DefaultServer:[202.106.184.166]
Address:202.106.184.166

>SetType = mx
>Sina.com.cn
DefaultServer:[202.106.184.166]
Address:202.106.184.166

Non-authoritativeAnswer:
Sina.com.cnMXPreference=10,MailExchanger=Sinamx.sina.com.cn

Sina.com.cnNameserver=Ns1.sina.com.cn
Sina.com.cnNameserver=Ns3.sina.com.cn
Sinamx.sina.com.cnInternetAddress=202.106.187.179
Sinamx.sina.com.cnInternetAddress=202.106.182.230
Ns1.sina.com.cnInternetAddress=202.106.184.166
Ns3.sina.com.cnInternetAddress=202.108.44.55

If the MX record of a domain name does not exist, a message similar to the following appears: 
C:/> nslookup
>SetType = mx
>Amaxit.com.cn
DefaultServer:[202.106.184.166]
Address:202.106.184.166

***202.106.184.166Can'tFindAmaxit.com.cn:Non-existentDomain 

  Use your own domain name in the email system
   Assume that your email server address is:61.176.1.120  
   A A record has been created:Mail.mydomain.comA61.176.1.120

If an MX record already exists 

If the MX record already exists and is found on a Domain Name Server, you need to contact your domain name service provider or the administrator of the Domain Name Server, modify the MX record as follows:

Your Domain NameInMX10Mail.mydomain.com 

The MX record does not exist. 

There are two ways to determine the exact DNS resolution of your domain name, one is to check the relevant application materials you submitted when registering the domain name, get the application accepted at that time, and contact the application accepting organization, so that the relevant personnel of the other party can help you find out; the other is obtained through NSLookup in WINNT, Win2000, or various UNIX operating systems. 

After finding your domain name server, please contact your domain name service provider or the administrator of the server to allow the Peer to add an MX record for you. The record format is as follows:

Your Domain NameInMX10Mail.mydomain.com 

Can I create an email system only with the Host Name?

Yes. Assume that the host name of your email server isMail.mydomain.com, that is, resolve mail.mydomain.com to yourThe IP address of the email server. You can createMail.mydomain.com domain. Your email format isUser1@mail.mydomain.com,Other email systems can send emails to your server. Dynamic domain names are also pointed. If you have a static IP address, you can even create an email system with an IP address ending with one.In another case, your domain name directs directly to your email server, that is, mydomain.com is resolved to your email server on the internet. At this time, you create a domain named mydomain.com,Your email format isUser1@mydomain.com 
 
What is RBL? 

RBLFull name:Real-timeBlackholeLists,It is a service provided by overseas anti-spam organizations to check the addresses of spammers,RBLFunctions are almost unavailable to Chinese users.Because we found that most IP addresses in China areRBLDatabase. Do not enable RBLFunction.Common RBL server addresses include:Relays.ordb.org dnsbl.njabl.org bl.spamcop.net sbl.spamhaus.org dun.dnsrbl.net dnsbl.sorbs.net 

To query and delete IP addresses in RBL, go to http://openrbl.org/AndHttp://ordb.org