This topic describes the terms of MX, CNAME, and TXT records and the time when domain name resolution takes effect.
1. MX
The abbreviation of MX is Mail Exchanger, which points to a mail server used by the e-mail system to locate the mail server according to the recipient's address suffix when sending emails.
Meaning of priority
MX priority doesn't make sense when only one MX record exists. When multiple MX records exist in your domain DNS records, the server of senders will deliver the email to the server with the highest priority. When this server fails and cannot receive the email, the server of the sender will automatically select the next server with the highest priority until the email is delivered successfully, or all servers cannot deliver the email and resulti in an undeliverable error.
How to check if MX record exists
A very useful tool for DNS MX record queries is nslookup, which can be used to query various record information in DNS. You can directly run nslookup under the Windows Command Prompt to enter an interactive mode, where you can query various types of DNS data.
DNS resolution data can be of various types, including SOA type data for setting the parameters of this zone, A type data for setting the IP address corresponding to the name, and MX type data for setting mail exchange. These different types of data can be queried through the interactive mode of nslookup. During the query, you can use the set type command to set the corresponding query type.
As shown in the following figure, you can use the command nslookup -qt=MX domain name to query if MX record is set.
Alibaba Mail MX Records:
Mail server |
Host |
Priority |
Record value |
@ |
MX |
5 |
mx1.sg.aliyun.com |
@ |
MX |
10 |
mx2.sg.aliyun.com |
MX record added in Alibaba Cloud DNS as shown in the figure:
2. CNAME
CNAME is an alias record, which allows you to map multiple names to the same computer.
For example, if the CNAME of "mail.domain name" points to "mail.sg.aliyun.com", you can use the "mail.domain name" form to access the Alibaba Mail login page.
Alibaba Mail CNAME Records:
Mail server |
Host |
Priority |
Record value |
CNAME |
- |
mail.sg.aliyun.com |
Alibaba Cloud DNS add a CNAME record as shown in the following figure:
3. SPF
SPF is the abbreviation of Sender Policy Framework, which is a technology that authenticates the identity of the sender with an IP address. It is a very efficient spam solution. The receiving party will first check the SPF record of the domain name to determine whether the sender's IP address is included in the SPF record. If so, it will be considered as a correct mail, otherwise it will be considered as a fake mail for return.
Alibaba Mail TXT Record Values
"v=spf1 include:spf.sg.aliyun.com -all"
How to setup the SPF record?
To improve the success rate of sending emails to a foreign domain, we recommend that you set a TXT record for your email domain.
SPF Recrod added in Alibaba Cloud is shown in the figure:
If you are not using Alibaba Cloud, we recommend that you consult the service provider where your domain name is located to find a specific method for adding TXT records.
4. Time in Force
There are many Internet nodes and DNS servers in the world. After you set the domain name resolution, it will be synchronized to all DNS servers in the world. And the time required for this process is the time when the resolution takes effect. The time when the domain name resolution takes effect can be divided into the following three scenarios:
1. Add the time when the new DNS records takes effect. Use the Alibaba Cloud DNS to add DNS records will take effect in real time.
2. Modify the time when the new DNS records takes effect. If you modify the records in Alibaba Cloud DNS, the final effect time depends on the cache refresh time of the DNS server(the DNS of each ISP caches the previous records before the modification and will not be updated in real time). Generally, it is equivalent to the TTL time when you set the resolution. For example, in your previous resolution setting, the TTL value is set to 10 minutes. After you modify the resolution, it will take effect globally within 10 minutes.
3. After modify the DNS, set the time when the new DNS records takes effect. If you use the Alibaba Cloud DNS to modify the DNS resolution after change DNS address. The final effective time also depends on the DNS server cache refresh time of each carrier. However, the refresh time of DNS in different regions is inconsistent and the refresh time is long. As a result, it takes 24 to 48 hours for the resolution to take effect globally. It takes 48 hours for international domain names such as. com and 24 hours for domestic domain names such as. cn.