DMARC (Domain-based Message Authentication, Reporting & Conformance) is an email authentication protocol that helps protect email senders from phishing attacks by verifying that emails are coming from the authorized sender. One of the key features of DMARC is the ability to set different policies for subdomains, allowing you to tailor your DMARC protection to the specific needs of each subdomain.
Why Use Different DMARC Records for Subdomains?
There are several reasons why you might want to use different DMARC records for subdomains:
- To protect different types of email: You may have different types of email coming from different subdomains, such as marketing emails from one subdomain and transactional emails from another. By setting different DMARC policies for each subdomain, you can ensure that each type of email is protected according to its importance and risk profile.
- To isolate issues: If there is a problem with one subdomain, such as a compromised email account, you can use DMARC to quarantine or reject emails from that subdomain without affecting emails from other subdomains. This can help to limit the damage caused by the issue.
- To comply with different regulations: Some industries or regions may have specific regulations regarding email authentication. By setting different DMARC policies for subdomains, you can ensure that you are complying with all applicable regulations.
How to Use Different DMARC Records for Subdomains
To use different DMARC records for subdomains, you will need to publish a DMARC record for each subdomain that you want to protect. The DMARC record for each subdomain should include the following tags:
- v=DMARC1: This tag indicates that the record is a DMARC record version 1.
- p=none|quarantine|reject: This tag specifies the DMARC policy for the subdomain. The three possible values are:
- none: Mail receivers should not take any action against emails that fail DMARC authentication for this subdomain.
- quarantine: Mail receivers should quarantine emails that fail DMARC authentication for this subdomain.
- reject: Mail receivers should reject emails that fail DMARC authentication for this subdomain.
- sp=none|quarantine|reject: This tag specifies the DMARC subdomain policy. This tag is optional, but if it is present, it will override the p tag for subdomains of this subdomain.
Here is an example of a DMARC record for a subdomain:
v=DMARC1; p=reject; sp=quarantine; rua=mailto:[email protected]
This record specifies that all emails from the subdomain should be rejected if they fail DMARC authentication. However, emails from subdomains of this subdomain will only be quarantined if they fail DMARC authentication.
When using different DMARC records for subdomains, it is important to keep the following in mind:
- You should not set a more permissive policy for a subdomain than for its parent domain. For example, if the parent domain has a policy of reject, then the subdomain should not have a policy of none or quarantine.
- You should monitor your DMARC reports to ensure that your policies are working as expected.
- You should be prepared to adjust your policies as needed. As your email infrastructure changes, you may need to update your DMARC policies to reflect those changes.
Using different DMARC records for subdomains can be a powerful way to improve your email security. By following the best practices outlined above, you can ensure that your DMARC policies are effective in protecting your organization from phishing attacks.