What causes DMARC bounces and SendGrid authentication issues?
Matthew Whittaker
Co-founder & CTO, Suped
Published 10 Jul 2025
Updated 17 Aug 2025
8 min read
Dealing with DMARC bounces and email authentication issues can be incredibly frustrating, especially when you’re relying on a service like SendGrid for your email campaigns. I’ve seen many businesses struggle with emails not reaching the inbox, often due to underlying DMARC, SPF, or DKIM problems. When emails fail authentication, they’re likely to be rejected or sent straight to the spam folder, impacting your sender reputation and critical communications.
The core of these issues often lies in the intricate interplay of these email authentication protocols. It’s not just about having the records in place, but ensuring they’re correctly configured and aligned with your sending practices. A single misstep can lead to widespread delivery failures.
In this article, I want to explore the common reasons behind DMARC bounces and authentication issues, with a particular focus on challenges faced by Twilio SendGrid users. My goal is to equip you with the knowledge to diagnose and fix these problems, helping you achieve better inbox placement and maintain a strong sending reputation.
DMARC, or Domain-based Message Authentication, Reporting, and Conformance, is a crucial email authentication protocol built upon SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail). Its primary role is to protect your domain from unauthorized use, such as spoofing and phishing, by telling receiving email servers what to do with messages that don't pass SPF or DKIM authentication.
SPF works by allowing domain owners to publish a list of authorized sending IP addresses in their DNS records. When an email is received, the server checks if the sending IP address is on that list. If it isn't, the SPF check fails. DKIM, on the other hand, adds a digital signature to your emails, which receiving servers can verify using a public key published in your DNS. This ensures the email hasn't been tampered with in transit.
For DMARC to pass, either SPF or DKIM (or both) must align with the From: domain of your email. This alignment is key. If the domains don't align, even if SPF and DKIM technically pass, DMARC will still fail, leading to bounces or messages being sent to spam. This is a common point of confusion for many senders, as I've observed in numerous cases where SPF and DKIM technically pass, but DMARC still fails.
DMARC bounces and authentication issues stem from several common sources. One of the most frequent is a DMARC verification failed error, which usually points to problems with SPF or DKIM alignment. For instance, if you're using a third-party email service provider (ESP) and your From: address domain doesn't match the domain SPF or DKIM is authenticating against, DMARC will fail.
Another common culprit is incorrect DNS record setup for SPF and DKIM. Even a small typo or an outdated record can lead to authentication failures. Additionally, email forwarding can sometimes break DMARC, as the forwarded email might not maintain the original authentication paths, leading to misalignment.
Sometimes, you might encounter DMARC TempErrors, which are temporary authentication issues. While these don't lead to immediate rejections, they can signal underlying problems that might escalate if not addressed. These SPF TempError or DKIM temporary errors often suggest transient network issues or problems with the DNS server. Persistent temporary errors can still negatively affect your sending reputation over time.
Another factor that can cause DMARC failures, and potentially land your emails on a blocklist (or blacklist), is email content. While not directly related to authentication, if your email content is flagged as spam, even perfectly authenticated emails can be filtered or rejected. This reinforces the need for a holistic approach to email deliverability, encompassing not just technical setup but also content quality and list hygiene.
SendGrid and DMARC authentication
Many of the DMARC bounce and authentication problems I see are related to using an email service provider (ESP) like SendGrid. While SendGrid is a robust platform, improper setup can lead to significant deliverability headaches. A frequent issue is when DMARC policies cause misalignment with the From domain. SendGrid uses CNAME records to delegate SPF and DKIM authentication to their servers. If these CNAMEs aren't correctly published or propagated, your emails won't authenticate properly.
I’ve encountered situations where SendGrid's own domain, for example, em1XX3.sendgrid.net, appears in the authentication headers instead of the sender's domain. This happens if the SendGrid setup isn't fully aligned. When SendGrid's domain is used for authentication and your From: address is yourdomain.com, a DMARC failure is inevitable due to domain misalignment.
Another specific issue with SendGrid can be related to how they handle bounced emails or email delivery failures from DMARC. Services like Gmail, AOL, or Yahoo have tightened their DMARC requirements, preventing emails with these domains in the From: address from being sent via third-party ESPs. If you are using a gmail.com from address with SendGrid, it will fail DMARC because the DMARC policy for gmail.com is set to reject.
Proper SendGrid domain authentication is critical. Ensure you've followed their instructions to the letter for adding CNAME records. This not only helps with DMARC but also significantly boosts your overall email deliverability.
Diagnosing and resolving issues
When facing DMARC bounces and authentication issues, a systematic approach to troubleshooting is essential. I always start by checking the DMARC reports. These XML reports, sent to the email address specified in your DMARC record, provide invaluable insights into why your emails are failing authentication and whether it's due to SPF, DKIM, or alignment issues. You can also troubleshoot DMARC reports from Google and Yahoo.
Next, I verify the DNS records for SPF and DKIM. Incorrect syntax, missing records, or improper values can all lead to failures. Use a reliable email deliverability tester to check your domain's authentication status. Specifically for SendGrid, confirm that their required CNAME records are present and correctly configured in your DNS. These records are critical for SPF and DKIM delegation to SendGrid's infrastructure.
Reviewing email headers of bounced messages is another critical step. The Authentication-Results header will tell you which checks passed or failed and why. If you see SendGrid's domains in the DKIM authentication results when your own domain should be there, it indicates an alignment issue specific to your SendGrid setup. You can also debug DMARC authentication failure using these reports.
Finally, monitor your DMARC reports regularly using a DMARC monitoring solution. This proactive approach allows you to quickly spot new issues or changes in authentication behavior, like sudden DMARC bounces from specific mailbox providers, and address them before they significantly impact your deliverability. For example, Google and Microsoft have introduced new sender requirements that emphasize the importance of robust DMARC implementation and consistent authentication.
Achieving consistent inbox placement
Resolving DMARC bounces and SendGrid authentication issues is a critical step towards maintaining high email deliverability. It demands a thorough understanding of SPF, DKIM, and DMARC, coupled with diligent monitoring and quick action when problems arise. By ensuring your authentication records are impeccable and aligned, you protect your sender reputation and ensure your legitimate emails reach their intended recipients.
Remember, email authentication protocols are constantly evolving, with providers like Outlook tightening their requirements. Staying informed and proactively managing your domain's authentication status is the best defense against unexpected bounces and blocklist (or blacklist) placements. This proactive approach is key to achieving consistent inbox placement in today's email landscape.
Views from the trenches
Best practices
Always set up a DMARC record, even with a p=none policy, to start receiving reports and understanding your email traffic.
Regularly monitor your DMARC reports for anomalies, such as sudden spikes in failures or unexpected sending sources.
Ensure that SPF and DKIM are properly configured and aligned for all domains and subdomains used for sending emails.
If using an ESP like SendGrid, follow their specific domain authentication instructions to the letter to ensure full alignment.
Common pitfalls
Failing to implement DMARC, SPF, and DKIM leaves your domain vulnerable to spoofing and can lead to emails landing in spam.
Incorrectly configuring CNAME records for ESPs, leading to misalignment between your 'From' domain and the authentication domain.
Ignoring DMARC reports, missing critical insights into authentication failures and potential malicious activity.
Using generic 'From' addresses from public domains (like Gmail or Yahoo) with third-party ESPs, which will inevitably fail DMARC.
Expert tips
Implement a DMARC policy with a p=quarantine or p=reject setting for stricter domain protection once you are confident in your DMARC setup.
Use a DMARC monitoring service to automate report collection and analysis, making it easier to identify and resolve issues.
Perform regular email deliverability tests to check your sender reputation and ensure your emails are consistently reaching the inbox.
Educate your team on email authentication best practices to avoid common mistakes that can lead to deliverability problems.
Marketer view
Marketer from Email Geeks says they noticed DMARC bounces on every domain they manage, all with a reject policy, suddenly failing between 8 PM and midnight, indicating a widespread issue for them.
2024-07-23 - Email Geeks
Expert view
Expert from Email Geeks says that DMARC bounces are typically specific to a particular sending domain or, less commonly, a particular receiving mailbox provider.
SendGrid for your email campaigns. I’ve seen many businesses struggle with emails not reaching the inbox, often due to underlying DMARC, SPF, or DKIM problems. When emails fail authentication, they’re likely to be rejected or sent straight to the spam folder, impacting your sender reputation and critical communications.
Twilio SendGrid users. My goal is to equip you with the knowledge to diagnose and fix these problems, helping you achieve better inbox placement and maintain a strong sending reputation.
Gmail, 
AOL, or 
Yahoo have tightened their DMARC requirements, preventing emails with these domains in the From: address from being sent via third-party ESPs. If you are using a gmail.com from address with SendGrid, it will fail DMARC because the DMARC policy for gmail.com is set to reject.
Google and 
Microsoft have introduced new sender requirements that emphasize the importance of robust DMARC implementation and consistent authentication.
Outlook tightening their requirements. Staying informed and proactively managing your domain's authentication status is the best defense against unexpected bounces and blocklist (or blacklist) placements. This proactive approach is key to achieving consistent inbox placement in today's email landscape.
