DMARC stores data specifying how email recipients should verify incoming messages for authenticity using the Domain Name System (DNS). However, how receivers use DMARC when subdomains are involved is one of the lesser understood parts of DMARC. While it may appear straightforward at first, the behavior may get complex.
There are a few critical aspects to grasp while dealing with subdomains. In this article, we'll look at the first issue, which is how the DMARC policy records are queried. In other words, which DNS TXT entries are checked by receivers?
Basic rules of email transmission and DMARC
- Receivers look for DMARC records based on the domain in the RFC5322 From address, also known as the 'From' address.
- Receivers will only perform one or two DNS requests to find a DMARC record for a message.
- If the message's From address contains a subdomain, the DMARC policy specified on that subdomain's parent domain only applies if the parent domain is the 'organizational domain' (see below) and no DMARC policy is defined for the subdomain. Any additional domains in the tree's DMARC policies are ignored.
The lookup procedure is terminated if a DMARC record is located at the first DMARC record domain. No additional DMARC record requests are conducted, and the DMARC record acquired from DNS for that domain is utilized for DMARC processing. If no DMARC record is available, the receiver may look for a DMARC record in another domain. DMARC provides the concept of 'organizational domain' to define this second location. While the definition is rather complicated, the procedure for identifying the organizational domain is essential as follows:
- Take the domain from the address in the 'From' field.
- Check the public suffix list for the domain's biggest suffix. The suffix for.com,.edu, and many other prominent TLDs are just the TLD itself.
- Keep one label after the public suffix and discard the others.
The sp tag
Unless a DMARC record has been published for a single subdomain, the DMARC policy specified for an organizational domain will apply to all subdomains by default. Domain owners, on the other hand, can use the "sp" tag to specify distinct rules for all subdomains (for subdomain policy).
It has the same syntax as the p tag. sp=none instructs email recipients that, regardless of the policy selected for the organizational domain, they should employ a policy of "none" for subdomains. Receivers are told to quarantine failed messages from subdomains when they see sp=quarantine, and they are told to reject them when they see sp=reject.
Working with subdomains
Subdomains must be safeguarded through enforcement procedures. Spoofers can send messages from email.company.com if company.com is set to p=reject but email.company.com is set to p=none. In this situation, even with an organizational p=reject, spoofers may mimic the brand and create all of the issues that DMARC is supposed to alleviate since DMARC was not implemented consistently across the domain.
Your organization may not utilize subdomains to send an email, but receivers are unaware. As a result, these subdomains can be just as effective as the main domain as impersonation vectors. In this scenario, DMARC is analogous to sunscreen: It is only effective where it is used. Therefore, you must use it everywhere.
Read Also : https://www.reddit.com/user/emailauth-io/comments/siir1l/how_dmarc_handles_subdomains_and_the_sp_tag/
Moreover, it's quite simple to accomplish. Put p=reject on your corporate domain and don't change it on any subdomains. You are now completely secured, and no one may send you emails without your specific permission! This may seem self-evident, but we regularly encounter unprotected subdomains in the wild, which might negate the anti-impersonation and anti-fraud advantages of bringing DMARC to enforcement.
Furthermore, if the brand-enhancing features of BIMI are of importance to you, you must have DMARC enforced on your organizational domain—without sp=none—in order to benefit from this new standard.Take precautions. Keep your brand safe. Keep your consumers safe. Keep your staff safe. Don't make your subdomains vulnerable to impersonation. Implement DMARC today using EmailAuth.
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In the fiercely competitive cyber world, it is necessary that you do your marketing well but, at the same time, pivotal that you’re aware of the basic security measures to safeguard your email sending habits.
Reverse DNS (PTR)SPF (Sender Policy Framework)DKIM (DomainKeys Identified Mail)DMARC (Domain-based Message Authentication, Reporting, and Conformance) REVERSE DNS A DNS query for the domain name associated with a particular IP address is known as a reverse DNS lookup.
This achieves the inverse of the more widely used forward DNS lookup, which queries the DNS system for an IP address.Reverse DNS lookups seek for a PTR (pointer) record on DNS servers.
If the server doesn't have a PTR record, it won't be able to resolve a reverse lookup.
PTR records include IP addresses with their segments reversed and ‘.in-addr.arpa’ appended to them.
Sender Policy Framework (SPF)Sender Policy Framework (SPF) is an email authentication protocol that allows domain owners to specify which email servers are permitted to send emails from their domain(s).
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Several problems may occur when implementing these protocols for your domain.
It is restricted, however, to identifying a forged sender claim in the email’s envelope, which is used when the email bounces.
When used in conjunction with DMARC, SPF detects email spoofing, a typical phishing scheme in which the email address or domain name of a reputable firm or trusted acquaintance is used.
This restriction helps mailbox providers use fewer resources while verifying SPF data.
If you surpass this limit, the SPF check will fail.
Each include statement in the originating SPF record and any SPF records pointed to counts toward the maximum of ten.Also Read:- How are DMARC, DKIM and SPF different from each other?You must also verify that each include statement in your SPF record is relevant and absolutely cannot be substituted by another method such as the ip4 and ip6 mechanisms.Implement ip4 and ip6 mechanismsWhen you have the opportunity, replace your include statement with the ip4 or ip6 mechanism to minimize the number of DNS lookups.
The most commonly used technical term DMARC is the abbreviation for Domain-based Message Authentication Reporting & Conformance.
It is a modus operandi that makes the use of Sender Policy Framework (SPF) and Domain Keys Identified Mail (DKIM) in order to identify the legitimacy of a message in the form of an email.
