MX records, a records, and reverse resolution for EDM emails

Zheng Yi 20110330

Background:

What is MXRecord?

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 forward resolution?

For example, the domain name www.55tuan.com you registered on hichina adds an MX record to the domain name management interface after you log on to hichina, pointing to the email server 121.11.24.146. This is called forward resolution.

What isRecord?

The A (Address) record is used to specify the IP address record corresponding to the Host Name (or domain name. You can direct the website server under this domain name to your web server. You can also set a subdomain name.

What is reverse resolution?

There are two regions in the DNS server: "forward lookup area" and "reverse lookup area". Reverse lookup area is IP reverse resolution, it is used to query the PTR record of an IP address to obtain the domain name pointed to by the IP address.

For example, use a info@news.gaopeng.com as the sender to send mail to the user's mailbox a@163.com. When Netease's email server receives this email, it will view the email header. The email header displays the IP address of the email, for example:

Received: From mta406.us.news.gaopeng.com
(Mta406.us.news.gaopeng.com [208.50.56.68])

Then 208.50.56.68 is the IP address of the SMTP server that sends the mail. Then, perform reverse resolution based on the IP address. If reverse resolution is performed, the domain name corresponding to this IP address is indeed mta406.us.News.gaopeng.com
Then accept this email. If reverse resolution finds that this IP address does not matchNews.gaopeng.com, Then the email is rejected.

Note 1: A of the domain name for reverse resolutionThe record must point to this IP address.

Note 2: Reverse resolution has nothing to do with the domain name registrar, it is to assign you an IP addressAddress IDCData Center. So sometimes there will be charges.

The reverse parsing process can be simulated in Windows as follows:

Command line:NSLookup-Qt = PTR

Enter the IP address you want to query, as shown below:

> 208.50.56.68

Non-authoritative response:

68.56.50.208.in-ADDR. ARPA
Name = mta406.us.news.gaopeng.com

What is an SPF record?:

The full name Is Sender Policy Framework, which is the sender's policy architecture. It is usually called SPF directly.

SPF is a DNS record type proposed to prevent spam. It is a TXT record used to register all IP addresses owned by a domain name for external mail.

For example, you can use NSLookup to view the SPF record of Meituan:

C: \>NSLookup

> Set
Type = txt

> Meituan.com

Non-authoritative response:

Meituan.com
TEXT =

 

"V = spf1 ip4: 58.83.134.133/27 ip4: 59.151.43.32/27 ip4: 211.151.229.32/27 I

P4: 211.151.229.64/26
Ip4: 211.151.229.128/28 ip4: 173.45.234.162 ip4: 173.45.238.15

5 ip4: 72.14.188.19
Include: aspmx.googlemail.com-all"