How important is an external email verifier on DMARC?
Matthew Whittaker
Co-founder & CTO, Suped
Published 20 Jul 2025
Updated 16 Aug 2025
8 min read
When setting up DMARC, we often focus on the core record: the policy for handling unauthenticated emails and where to send aggregate (RUA) or forensic (RUF) reports. However, a crucial, yet sometimes overlooked, aspect is the external email verifier, specifically for DMARC reports directed to domains you don't directly control. This verification mechanism ensures that the domain receiving the reports (the recipient domain) has explicitly authorized the sending of those reports, preventing potential abuse.
While not all DMARC report generators strictly enforce this external verification, it's considered a best practice for maximizing report delivery and maintaining security. Understanding its purpose and how to implement it correctly can significantly enhance your ability to monitor your domain's email ecosystem and prevent spoofing.
Understanding external domain verification for DMARC reports
DMARC reports provide invaluable insights into email traffic, helping identify legitimate sending sources and detect malicious activity like phishing or spoofing. These reports are typically sent to an email address specified in your DMARC record's rua (aggregate reports) or ruf (forensic reports) tags. When these email addresses belong to a domain different from the one publishing the DMARC record, an external verification mechanism comes into play.
This mechanism, also known as external destination verification, involves placing a special DNS TXT record on the domain that will be receiving the DMARC reports. Its primary purpose is to prevent an attacker from maliciously directing DMARC reports from an unsuspecting domain to an email address they control, potentially overwhelming or spamming that inbox. It's a security measure to ensure explicit consent for receiving such reports.
The DMARC rua and ruf tags in your DMARC record specify the destination for these reports. For instance, if your DMARC record is on example.com and you want reports sent to aggregate@thirdparty.com, a verification TXT record needs to be added to thirdparty.com. This record typically confirms that thirdparty.com is prepared to receive DMARC reports for example.com.
The format for this verification record is detailed in DMARC's RFC 7489, specifically in section 7.1. Without this explicit verification, some DMARC-compliant receiving mail servers might simply refuse to send reports to the external domain, even if your DMARC policy is set up to request them.
The importance of comprehensive DMARC reporting
One of the interesting complexities with external DMARC report verification is the varied implementation among different mail service providers. Some large providers, like Google, might not require this explicit verification for sending DMARC aggregate reports, while others, such as Yahoo!, might enforce it. This discrepancy can lead to an incomplete picture of your DMARC compliance if you rely on reports from multiple sources.
The rationale behind requiring external verification is largely rooted in preventing abuse, such as mailbombing. An attacker could theoretically point a DMARC record to an email address they don't own, causing a flood of DMARC reports to that address. The explicit TXT record verification serves as a safeguard against this. While IETF standards encourage this verification, practical implementation varies. For example, some mail service providers may implicitly trust commercial DMARC report aggregators to handle report volume responsibly.
Despite these inconsistencies, the general recommendation remains to implement the external verification record. It's a minimal effort that can significantly improve the comprehensiveness of your DMARC reporting. This enables a more complete view of your email sending infrastructure and better troubleshooting of DMARC failures.
Best practice
Always implement the external email verifier for your DMARC rua and ruf tags, especially when using a third-party service to collect DMARC reports. This ensures you receive comprehensive data from as many mail receivers as possible.
Impact on report collection versus policy enforcement
While having an external email verifier (or not) does not directly impact whether your DMARC policy is honored, it profoundly affects your ability to receive all available DMARC reports. A DMARC policy, like p=reject, will still be applied by receiving servers regardless of whether they send you reports. The core function of DMARC, which is to instruct recipients on how to handle emails that fail SPF or DKIM alignment, operates independently of report generation.
However, the true value of DMARC lies in the visibility it provides. Without comprehensive reports, you're essentially flying blind. You won't know which legitimate emails are failing authentication, or how often malicious actors are attempting to spoof your domain. This lack of insight can hinder your efforts to improve email deliverability and protect your brand reputation effectively. Receiving reports from Google and Yahoo is critical for most senders.
The external verification record is particularly important for vendors or organizations that manage DMARC reporting for multiple client domains. Without it, they might only receive a subset of reports, making it challenging to provide a complete DMARC monitoring and enforcement service. This underscores why many DMARC service providers will guide you through setting up this record.
Without external verification
Report data: Incomplete DMARC aggregate reports received. Some mail service providers may withhold reports if verification is missing.
Visibility: Limited insight into spoofing attempts or legitimate email authentication failures across all mail receivers.
Policy enforcement: Your DMARC policy (p=none, quarantine, reject) will still be enforced by recipients, but you won't get full feedback.
With external verification
Report data: Comprehensive DMARC aggregate reports from nearly all major mail service providers.
Visibility: Full visibility into all email streams, making it easier to identify and mitigate issues and ensure DMARC for email and spam protection.
Policy enforcement: DMARC policy is enforced, and you receive the necessary feedback to adjust and enforce your policy to quarantine or reject.
Setting up the external verification record
Setting up the external email verifier involves creating a specific DNS TXT record on the domain designated to receive DMARC reports. The record's hostname typically follows the pattern yourdomain.com._report._dmarc.receivingdomain.com, with a value of v=DMARC1. This informs mail servers that the receivingdomain.com is authorized to accept DMARC reports for yourdomain.com.
Ensuring this record is correctly published is part of a robust DMARC, DKIM, and SPF setup. If you're using a DMARC monitoring service, they will typically provide the exact record you need to publish. It's also wise to check your DMARC reports regularly to see which providers are sending them and if any significant sources are missing. This can indicate a problem with your verification record or the provider's adherence to the DMARC standard.
While this verification step isn't universally enforced by all DMARC report generators, implementing it is a minimal effort that provides maximum benefits for your DMARC visibility. It helps ensure that you receive the fullest possible set of aggregate reports, which are essential for properly analyzing your email ecosystem and moving towards a stronger DMARC policy like p=quarantine or p=reject. This contributes to a stronger email domain reputation.
Mail service provider
External verification requirement
Impact on reports
Google
Often not strictly required
Reports may still be received even without verification.
Yahoo!
Typically required
Reports may be withheld if verification record is missing.
LinkedIn
Often not strictly required
Reports may still be received even without verification.
Mail.ru
Varies, some enforcement seen
Reports may be received, but consistency can vary without verification.
Beyond external verification for DMARC reports, keeping a close eye on your email blocklists is also important. Just as DMARC helps protect your domain from spoofing, avoiding being listed on a blocklist (or blacklist) ensures your legitimate emails reach the inbox. Both are critical for maintaining good email deliverability.
Views from the trenches
Best practices
Always set up the external verification record for your DMARC RUA/RUF tags to ensure comprehensive report collection.
Regularly review your DMARC reports to identify missing data or non-compliant senders who are not sending reports.
Use a DMARC monitoring service that automatically handles external verification where possible.
Ensure your DMARC policy aligns with your domain's sending patterns to avoid legitimate emails being flagged.
Verify all external sending sources are properly authenticated with SPF and DKIM before moving to enforcement policies.
Common pitfalls
Neglecting to publish the external verification record, leading to incomplete DMARC report data.
Assuming all mail service providers enforce external verification uniformly, leading to blind spots.
Not monitoring DMARC reports, thus missing insights into spoofing or legitimate email authentication failures.
Setting a DMARC policy too aggressively (e.g., p=reject) without sufficient data and monitoring.
Overlooking DMARC alignment issues from third-party sending services, impacting deliverability.
Expert tips
While the DMARC policy will always be honored, the ability to receive complete reports from all DMARC-compliant mail service providers is crucial for effective monitoring and enforcement.
The external verification record primarily prevents DMARC reports from being used for mailbombing or abuse.
Inconsistencies exist among mail service providers regarding the enforcement of external verification.
Even without external verification, your DMARC policy will still be applied, but your visibility into unauthenticated traffic will be limited.
Implementing external verification is a simple step that significantly enhances the reliability of your DMARC reporting.
Expert view
Expert from Email Geeks says some report senders will require external verification, but many, like Google, do not. It is best current practice to add it for the most comprehensive reports.
2022-02-25 - Email Geeks
Marketer view
Marketer from Email Geeks says they check external verification, and that it helps prevent attackers from using DMARC reports to mailbomb innocent third parties.
2022-02-25 - Email Geeks
Conclusion: why external verification matters
The external email verifier for DMARC, particularly the TXT record that authorizes an external domain to receive DMARC reports, is a critical component for achieving full visibility into your email ecosystem. While its enforcement varies among mail service providers, its implementation is a low-effort, high-reward step that ensures you receive the most complete data possible. This comprehensive reporting is essential for effective DMARC implementation and ongoing security.
By understanding the nuances of DMARC, SPF, and DKIM, including external verification, you empower your organization to proactively monitor email authentication failures and protect your domain from spoofing and phishing attacks. Don't let incomplete reporting hinder your email security efforts.
Google, might not require this explicit verification for sending DMARC aggregate reports, while others, such as 
Yahoo!, might enforce it. This discrepancy can lead to an incomplete picture of your DMARC compliance if you rely on reports from multiple sources.
LinkedIn
Mail.ru
