Why are emails failing DMARC alignment with Symantec Email Security Cloud after a DMARC policy update to p=reject?
Matthew Whittaker
Co-founder & CTO, Suped
Published 13 May 2025
Updated 19 Aug 2025
9 min read
Updating your DMARC policy to p=reject is a critical step in enhancing email security. It tells receiving mail servers to reject emails that fail DMARC authentication and alignment checks, effectively stopping spoofing and phishing attempts using your domain. However, a common challenge arises when legitimate emails begin failing DMARC alignment, particularly with specific security solutions like Symantec Email Security Cloud. This can lead to unexpected bounces and prevent crucial messages from reaching their intended recipients.
I've encountered this exact scenario, where a sender's DMARC policy was updated to p=reject (or sp=reject), only to find emails bouncing specifically from recipients using Symantec. Despite extensive testing showing proper authentication and DMARC alignment with other providers, these particular bounces persisted. This strongly suggests a nuanced interaction between the sender's configuration and the receiving Symantec platform.
The problem can be puzzling because it doesn't affect all Symantec users, hinting at potential tenant-level configurations or specific processing quirks within the platform. Understanding why this happens requires a deeper dive into how DMARC works and how Symantec (now Broadcom) handles incoming mail flows, especially when a strict p=reject policy is in place. It’s also worth noting that when the policy was relaxed to p=quarantine, emails were delivered to the inbox (or at least quarantined), allowing some recipient engagement, which quickly ceases with a p=reject policy in effect.
DMARC, or Domain-based Message Authentication, Reporting, and Conformance, is an email authentication protocol designed to protect your domain from unauthorized use. It builds upon SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) by providing instructions to receiving mail servers on how to handle emails that fail authentication. These instructions are defined by the p tag in your DMARC record, which can be none, quarantine, or reject. Moving to p=reject is the strongest enforcement level.
For an email to pass DMARC, it must pass either SPF authentication with SPF alignment, or DKIM authentication with DKIM alignment. Alignment is crucial, meaning the domain in the From header (RFC5322.From) must match the domain used for SPF or DKIM. Without alignment, even if SPF or DKIM technically pass, DMARC will fail. This is often where the issue lies, as intermediary mail security solutions can alter an email in ways that break this alignment.
Symantec Email Security Cloud, like many other email security gateways, performs its own set of checks and, in some cases, modifications to incoming emails for security purposes. This can include rewriting URLs for anti-phishing protection or other content analysis. When these modifications occur after the DKIM signature has been applied by the sender, they can invalidate the signature, leading to a DKIM failure. If SPF also fails to align (perhaps due to forwarding or third-party sending services not correctly configured for SPF), the DMARC check will fail, and with a p=reject policy, the email will bounce.
Broadcom's documentation confirms that messages will fail DMARC if they fail both SPF (or SPF alignment) and DKIM (or DKIM alignment). This means their system will strictly enforce your p=reject policy if these alignment failures occur.
Unpacking DMARC alignment failures specific to Symantec
When emails fail DMARC with Symantec, the most common culprit is usually related to how the email's content or path is handled by the security solution. The issue of anti-phishing technology rewriting URLs is a prime suspect. This process involves Symantec (or any other email gateway) modifying links within the email body. While beneficial for security, it breaks the DKIM signature, as the cryptographic hash of the message content no longer matches the original signature. If no other valid authentication path (like SPF with alignment) is available, DMARC will fail.
Another significant factor is misconfiguration on the recipient's Symantec Email Security Cloud side. It's possible that the specific tenant experiencing bounces has a configuration that doesn't trust Symantec's own modifications, or perhaps it's not correctly configured to handle emails from your sending infrastructure after a DMARC policy update. This could include rules that don't account for your sending IPs or DKIM signing practices, leading to DMARC alignment failures even for legitimate emails.
Third-party sending services can also complicate DMARC alignment. If you're using a marketing automation platform or a transactional email service, ensuring their SPF and DKIM implementations correctly align with your From domain is essential. Symantec, like other DMARC-compliant receivers, will evaluate these authentication results. If the third party's setup causes an alignment issue, Symantec will apply your p=reject policy.
Troubleshooting DMARC failures and recipient engagement
Diagnosing these specific DMARC issues requires a multi-faceted approach. First, regularly check your DMARC reports. These reports (RUA and RUF) provide invaluable insights into how various mail servers, including Symantec's, are processing your emails and why they might be failing authentication and alignment. Pay close attention to the auth_results and policy_evaluated sections to pinpoint the exact failure points.
For specific issues with a service like Symantec Email Security Cloud, direct engagement with the recipient's IT team is often the most effective path. Ask them to check their Symantec logs for details on the bounced emails, specifically looking for the DMARC verdict and any reasons cited for the failure. They might also be able to adjust their Symantec configuration to trust your sending domain or whitelist specific sending IPs if necessary. It’s a common strategy, similar to how I’ve worked with Microsoft 365 customers facing similar challenges.
If you're still in the process of rolling out p=reject, consider a gradual approach. Starting with a p=quarantine policy allows you to monitor DMARC reports for failures without outright blocking emails. This provides a safety net while you identify and resolve authentication issues, especially with specific mail gateways or recipient configurations. You can then gradually increase the policy enforcement level.
Symantec Email Security Cloud (now part of Broadcom) is a robust platform, but its configurations can be complex. While the general principles of DMARC, SPF, and DKIM remain consistent, the specifics of how Symantec processes incoming mail can influence DMARC outcomes. One key consideration is how Symantec's internal processes might scan or modify an email, potentially breaking DKIM signatures or affecting SPF alignment, even if the modifications are done for legitimate security reasons.
It’s not uncommon for enterprise-level email security solutions to have features like URL rewriting or attachment sandboxing. These operations change the email content after it leaves your sending server but before it reaches the final recipient's inbox. Since DKIM relies on the integrity of the message content, any alteration post-signing will cause the DKIM signature to fail validation. If your emails are relying heavily on DKIM for DMARC alignment, this could be the root cause of the issue.
To effectively navigate this, collaborate closely with the Symantec Email Security Cloud administrators at the recipient's organization. They have the necessary access to review their specific policies, logs, and potentially adjust settings that impact how DMARC is evaluated for your domain. This might involve creating exceptions or tuning their anti-phishing features to account for legitimate emails from your domain that are DMARC compliant but undergo Symantec’s internal modifications.
Views from the trenches
Best practices
Ensure SPF and DKIM are correctly configured and aligned for all your sending domains and third-party senders. Test your configurations thoroughly.
Deploy DMARC gradually, starting with `p=none` for monitoring, then `p=quarantine`, before moving to `p=reject`.
Utilize DMARC aggregate and forensic reports to identify authentication failures and sources. This data is critical for troubleshooting.
Common pitfalls
Rushing to `p=reject` without thorough monitoring can lead to legitimate emails being blocked or blacklisted.
Ignoring DMARC reports, which contain vital information about authentication failures and sources.
Not accounting for third-party email service providers' SPF and DKIM alignment in your DMARC policy.
Expert tips
If Symantec is causing issues, ask the recipient to check their Symantec logs for details on DMARC failures and any specific rules that might be applying. There might be a tenant-level misconfiguration.
Sometimes, anti-phishing technologies rewrite URLs, breaking DKIM. Check if the recipient's Symantec setup has such a feature enabled and if it's configured to trust your domain's changes.
When moving to `p=reject`, if emails are still arriving in the inbox even if quarantined, it suggests recipients might be manually releasing them from spam. Bouncing emails means no chance of engagement.
Expert view
Expert from Email Geeks says to ask the sender to find a friendly recipient and have them escalate the issue through their Symantec (Broadcom) support chain. A systems integration issue is more likely than a bug, possibly due to declining documentation or training standards.
2023-02-23 - Email Geeks
Expert view
Expert from Email Geeks says that this scenario sounds like anti-phishing technology that rewrites URLs, causing content changes and thus breaking DKIM. It's important to find a friendly recipient and ask if their company uses such a solution. If you can get the content, you might be able to see it yourself.
2023-02-23 - Email Geeks
Ensuring DMARC success with a p=reject policy
Moving to a p=reject DMARC policy is a significant step towards a more secure email environment, protecting your brand and recipients from malicious actors. However, it's a step that requires careful planning, continuous monitoring, and readiness to troubleshoot unexpected deliverability issues, especially when interacting with diverse email security gateways like Symantec Email Security Cloud.
When legitimate emails fail DMARC alignment, particularly with Symantec, it often points to an interaction between their mail processing and your authentication methods. By focusing on proper SPF and DKIM alignment, leveraging DMARC reports, and engaging directly with recipient IT teams, you can diagnose and resolve these issues, ensuring your emails reliably reach their destination, even under the strictest DMARC policies.
Symantec Email Security Cloud. This can lead to unexpected bounces and prevent crucial messages from reaching their intended recipients.
Microsoft 365 customers facing similar challenges.
