When setting up domains and email services, it’s essential to grasp how different DNS records interact. The MX (Mail Exchange) and A (Address) records are two of the most fundamental records in this process. Let’s delve into how these records work, especially in email delivery.
The Role of MX Records
MX stands for Mail Exchange. An MX record directs where emails sent to a particular domain or subdomain should be delivered. Think of it as a mail-forwarding address. When you send an email, your email server checks the MX record of the recipient’s domain to determine where to send that email.
Example:
If you have an MX record like this:
postmark.dev.cordero.me 10 inbound.postmarkapp.com.
Any email sent to user@postmark.dev.cordero.me will be forwarded to the servers at inbound.postmarkapp.com.
The “10” before the server address is the priority. If multiple MX records exist, the one with the lowest number is tried first.
The Role of A Records
An A record, or Address record, maps a domain or subdomain to an IP address. When you type a URL into your browser, the A record tells your browser which IP address it should connect to.
However, in the email, the A record plays a different role. After finding the MX record for the destination, the sending email server will look up the A record of the destination provided by the MX record to get the IP address to which it should deliver the email.
NOTE:
The A record for postmark.dev.cordero.me does NOT get used. In fact, there doesn’t need to be an A record.
Bringing It All Together
Let’s take our earlier example and add a hypothetical A record for clarity:
MX Record:
postmark.dev.cordero.me 10 inbound.postmarkapp.com.
A Record:
inbound.postmarkapp.com. A 123.1.1.222
Email Flow
1. You send an email to user@postmark.dev.cordero.me.
2. Your email server checks the MX record for postmark.dev.cordero.me and finds out it should deliver the email to inbound.postmarkapp.com.
3. To know where inbound.postmarkapp.com is located, the email server checks the A record for inbound.postmarkapp.com and gets the IP address 123.1.1.222.
4. Your email server connects to 123.1.1.222 and delivers the email.
Key Takeaways
The A record for the email’s recipient domain (e.g., postmark.dev.cordero.me in our example) is not consulted during email delivery.
The MX record tells where the email should go, while the A record of the MX’s target provides the actual IP address for that delivery.
While the A record isn’t directly involved in the email delivery process, it’s essential for other purposes, like accessing websites.
Conclusion
Grasping the interplay between MX and A records is essential for anyone involved in domain setup or email administration. By understanding how each record contributes to the email delivery process, you can ensure efficient and correct configuration for your domain.