How can I implement a strict DMARC policy without blocking Google Workspace emails?
Michael Ko
Co-founder & CEO, Suped
Published 14 Jun 2025
Updated 17 Aug 2025
7 min read
Implementing a strict DMARC policy, particularly p=reject, is an important step towards robust email security and combating phishing. However, this process can inadvertently lead to legitimate emails, especially those sent via Google Workspace, being blocked. This issue typically arises when not all legitimate sending sources for your domain are correctly authenticated with SPF and DKIM.
The key to successful DMARC implementation is a methodical, phased approach that prioritizes visibility and data analysis. Rushing to a p=reject policy without verifying all legitimate email flows can lead to severe deliverability problems, causing critical communications to fail.
This guide outlines the steps to safely implement a strict DMARC policy for your domain, ensuring your Google Workspace emails are delivered without interruption, while still protecting your domain from unauthorized use. We will focus on the technical configurations needed and the strategic decisions involved.
One of the most common reasons legitimate emails get blocked when implementing DMARC is skipping the crucial monitoring phase. Directly setting a DMARC policy to p=reject or p=quarantine without a clear understanding of all your email sending sources can lead to unintended blocking of valid mail streams. This is especially true for complex setups involving multiple third-party services alongside your primary Google Workspace environment.
Always begin with a p=none policy, also known as the monitor policy. This allows you to collect DMARC reports and identify all senders using your domain, without affecting email delivery. These reports are crucial for understanding which of your legitimate emails are failing authentication and why.
Before you even think about DMARC, ensuring robust SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) configurations is non-negotiable. DMARC relies on the successful authentication of at least one of these protocols. For Google Workspace, this means setting up SPF records that include Google's sending IP addresses and configuring DKIM via your Google Admin Console. Google provides clear instructions for both.
To set up DKIM for your Google Workspace domain, you generally generate a domain key within your Google Admin Console and then add it as a TXT record to your DNS. It is recommended to use a 2048-bit key for stronger security if your DNS host supports it, otherwise a 1024-bit key will suffice. This process ensures that emails sent directly from Google Workspace are properly signed and can pass DMARC authentication.
Your SPF record should include include:_spf.google.com. If you use other email sending services (ESPs or CRMs), their respective SPF include mechanisms must also be added to your domain's SPF record. Remember, SPF has a 10-lookup limit, so manage your includes carefully. For DKIM, each email sender (Google Workspace, your ESP, etc.) needs its own DKIM key and record for proper authentication.
The phased approach to DMARC policy
The transition to a strict DMARC policy (blocklist or blacklist) should always be gradual. Begin by publishing a DMARC record with a p=none policy. This instructs recipient servers to simply monitor unauthenticated emails and send reports to the specified address (RUA tag), rather than blocking them. This crucial monitoring phase allows you to identify all legitimate sending sources and resolve any authentication issues without impacting deliverability.
The DMARC record is a TXT record added to your DNS. Here's an example of a simple DMARC record with a p=none policy and reporting enabled:
After a period of monitoring (typically several weeks to a few months, depending on your sending volume and complexity), you can gradually transition to a stricter policy. The next step is usually p=quarantine, which instructs recipient servers to place unauthenticated emails in the spam or junk folder. Only once you are confident that all your legitimate emails are passing authentication should you move to p=reject, which tells servers to completely block (reject) unauthenticated mail.
DMARC policy
Action on failure
Impact on email delivery
p=none
Monitor unauthenticated emails, send reports.
No impact, emails are still delivered.
p=quarantine
Unauthenticated emails are sent to spam/junk folder.
Potential reduction in inbox placement.
p=reject
Unauthenticated emails are completely blocked.
Significant risk of blocking legitimate email if not configured correctly.
Ensuring alignment and covering all senders
A common mistake is assuming that setting up SPF and DKIM for your main Google Workspace account covers all your sending. This isn't true if you use other services to send emails on behalf of your domain. Each unique sender must properly authenticate emails to achieve DMARC alignment. DMARC requires either the From: header domain to align with the SPF domain or the DKIM signing domain. Failing to align all sending sources will result in DMARC failures, leading to emails being blocked or sent to spam.
If you are using a third-party Email Service Provider (ESP) or a CRM for marketing or transactional emails, you must configure SPF and DKIM specifically for that service. This often involves adding CNAME records provided by the ESP to your DNS. While some ESPs handle SPF via their include mechanisms in your SPF record, DKIM is almost always unique to each sender. Each ESP will provide specific instructions for their DKIM setup.
Another crucial aspect is understanding how DMARC policies apply to subdomains. If your main domain has a DMARC record, subdomains will inherit that policy unless you explicitly create separate DMARC records for them. This can be a concern if certain subdomains are used for specific sending purposes, like a transactional email subdomain, that might have different authentication needs.
Internal Google Workspace emails
Authentication: Rely on the SPF record including Google's mechanism (include:_spf.google.com) and DKIM configured directly within the Google Admin Console.
Alignment: Google automatically ensures SPF and DKIM alignment for emails sent directly through Google Workspace once properly set up.
Troubleshooting: If internal Google Workspace emails fail, double-check your DNS records and the status in your Google Admin Console. Consider using the Google and Yahoo compliance guide.
Third-party sending services
Authentication: Each third-party service (e.g., email marketing platforms, CRM systems) requires its own SPF include and a unique DKIM record. These are usually provided as CNAME records by the service.
Alignment: Ensure the From: domain aligns with either the SPF domain or DKIM signing domain provided by the ESP. Subdomain inheritance should also be considered.
Troubleshooting: If third-party emails are failing, verify the CNAME records for DKIM and confirm their inclusion in your SPF record. Check your DMARC aggregate reports to pinpoint the source of failures.
Monitoring and troubleshooting DMARC deployment
Once your DMARC record is published with p=none, the real work begins, or at least the real data collection begins. You will start receiving DMARC reports (RUA for aggregate reports and RUF for forensic reports) to the email address specified in your DMARC record. These reports are invaluable for understanding your email ecosystem. They detail which emails are passing or failing SPF and DKIM authentication, and from which IP addresses they are originating.
Analyzing these reports will help you identify any legitimate sending sources that are not yet properly authenticated. You might discover old systems or third-party services still sending emails from your domain that you were unaware of. Each of these unauthenticated sources needs to have SPF and DKIM configured, or be decommissioned, before you move to a stricter DMARC policy. This process requires diligence and attention to detail, but it's essential for preventing legitimate emails from being blocked.
Even with diligent setup, issues can arise. Common problems include misconfigured DNS records, SPF lookup limits being exceeded, or DKIM selectors not being properly propagated. If emails are still being blocked after transitioning to p=quarantine or p=reject, revert to a more relaxed policy (p=none) to prevent further disruption. Then, revisit your DMARC reports, re-evaluate all sending sources, and address any remaining authentication failures.
Views from the trenches
Best practices
Start with `p=none` and systematically verify all legitimate email sending sources before increasing policy strictness.
Ensure both SPF and DKIM are correctly configured and aligned for every service sending email on your domain, including Google Workspace.
Utilize DMARC aggregate (RUA) reports to gain comprehensive visibility into all email traffic using your domain.
Implement separate DKIM records for each email sending platform or service used, including Google Workspace and any third-party ESPs.
Common pitfalls
Directly deploying `p=reject` without prior monitoring leads to legitimate emails being blocked.
Failing to set up DKIM authentication for all third-party email service providers (ESPs) results in DMARC failures.
Neglecting to monitor DMARC reports, which causes missed authentication issues and potential deliverability problems.
Assuming that Google Workspace's default setup covers all DMARC authentication requirements for external senders.
Expert tips
Confirm that SPF and DKIM are fully functional for all senders, especially Google Workspace. This should be done before moving past a `p=none` policy.
If you manage a customer's domain and they are using subdomains, ensure explicit DMARC records are created for those subdomains if they don't inherit the main domain's policy.
Education on DMARC's function and how to analyze its reports is critical for preventing common implementation errors.
When troubleshooting DMARC issues, revert to `p=none` to stop legitimate emails from being blocked while you investigate and resolve authentication problems.
Marketer view
Marketer from Email Geeks says they started with a p=none policy and fixed authentication issues before moving to quarantine or reject.
2024-07-09 - Email Geeks
Expert view
Expert from Email Geeks says that the customer likely put the reject policy on the organizational domain, while the bulk sender manages a subdomain. It's crucial to review reports to ensure all traffic is properly authenticated.
2024-07-09 - Email Geeks
Ensuring successful DMARC enforcement
Successfully implementing a strict DMARC policy without blocking legitimate Google Workspace emails, or any other email, hinges on a meticulous and iterative approach. Start by establishing a solid foundation with correctly configured SPF and DKIM for all your sending services, especially Google Workspace itself. Then, transition through DMARC policies gradually, from monitoring to quarantine, and finally to reject, using the valuable insights from DMARC reports at each stage.
Google Workspace, being blocked. This issue typically arises when not all legitimate sending sources for your domain are correctly authenticated with SPF and DKIM.
