Why is Gmail rejecting unauthenticated email from gmail.com due to DMARC policy when sending via Sendgrid?
Matthew Whittaker
Co-founder & CTO, Suped
Published 30 May 2025
Updated 19 Aug 2025
8 min read
Many email senders, especially those new to email deliverability, encounter a puzzling issue: their emails from an @gmail.com address are rejected by Gmail due to DMARC policy even when sending through a reputable service like SendGrid. The error message typically states: "550-5.7.26 Unauthenticated email from gmail.com is not accepted due to domain's DMARC policy."
This can be confusing, particularly since Gmail's public DMARC record for its own domain (gmail.com) is often set to `p=none`. This policy normally suggests that receiving servers should not reject or quarantine emails that fail DMARC, but merely monitor them. So, why the rejection?
The challenge of sending from @gmail.com via SendGrid
The core of the issue lies in domain spoofing. When you use an @gmail.com address as your "From" address but send the email through a third-party email service provider (ESP) such as SendGrid, you are, in essence, trying to send mail that appears to originate from Gmail without Gmail's explicit authorization. SendGrid will correctly apply its own SPF and DKIM authentication to the email, but these will be for SendGrid's domain (e.g., sendgrid.net) or your verified sending domain, not gmail.com.
DMARC (Domain-based Message Authentication, Reporting, and Conformance) relies on alignment. For a message to pass DMARC, either the domain used in the SPF check or the domain signed by DKIM must align with the domain in the "From" header. When you send from @gmail.com via SendGrid, there's a misalignment because SendGrid's authentication doesn't match the "From" domain of gmail.com. This is why the email is flagged as "unauthenticated."
Using a freemail domain like gmail.com, yahoo.com, or aol.com for bulk or transactional email via third-party services is generally considered a poor practice and a spam indicator. Major mailbox providers have taken steps to curb this behavior because it's a common tactic for phishing and impersonation. While SendGrid might still allow you to configure this, it often leads to deliverability issues, including emails being sent to spam or outright rejected.
Gmail's internal DMARC enforcement
Even though gmail.com's official DMARC policy is `p=none`, this policy applies to *other* receiving mail servers. Google (as a mailbox provider) has the right to, and does, implement stricter internal rules for emails claiming to be from its own domain. They have a vested interest in preventing unauthorized use of the gmail.com domain to protect their brand, users, and the overall email ecosystem from phishing and spam.
This means that if an email appears to come from gmail.com but wasn't sent through Google's own authorized sending infrastructure (which includes proper SPF and DKIM authentication for gmail.com), Gmail will likely reject it, regardless of the public `p=none` policy. This isn't a new phenomenon, but it has become more consistently enforced over time, especially with the recent focus on email authentication standards for bulk senders by Gmail and Yahoo.
While some senders might observe this behavior only randomly or for a small portion of emails, it's a clear signal that Google is actively working to prevent the unauthorized use of its domain for sending. This proactive stance protects Gmail's reputation and helps ensure that legitimate emails from Gmail users are trusted.
The misconception
Many believe that because gmail.com has a `p=none` DMARC policy, emails failing DMARC should only be monitored, not rejected. This is generally true for *other* receiving mail servers.
This misunderstanding can lead to frustration when emails sent via ESPs using the gmail.com "From" address are rejected.
DMARC alignment and third-party sending services
DMARC works by checking if the domain used in the "From" header (the visible sender) aligns with the domains authenticated by SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail). For an email sent via a third-party ESP like SendGrid, the SPF check typically verifies SendGrid's sending IP, and DKIM verifies a signature applied by SendGrid using one of their domains (e.g., sendgrid.net).
The problem arises because the "From" domain is gmail.com, which is not the domain SendGrid is authenticating. This mismatch means that while SendGrid's authentication might technically pass for its own domain, it fails DMARC alignment with gmail.com. This is essentially what the "unauthenticated" part of the rejection message refers to, as it's unauthenticated for the stated From domain.
Sending with an owned domain
When you use your own domain (e.g., yourdomain.com) as the "From" address and configure SPF/DKIM records in your DNS to authorize SendGrid (or any ESP) to send on your behalf, DMARC alignment can be achieved. This means the authenticated domain matches your "From" domain.
Reputation control: You maintain full control over your sending reputation.
Improved deliverability: Emails are more likely to reach the inbox, reducing bounces and spam flagging.
Sending with a freemail domain via an ESP
When you use a freemail domain like gmail.com as your "From" address through an ESP, the email fails DMARC alignment for the "From" domain, even if the ESP properly authenticates its own domain.
No control: You have no control over the freemail domain's policies or reputation.
Deliverability issues: Emails are frequently rejected or sent to the spam folder due to lack of authentication and alignment.
This DMARC failure is why Gmail (and other mailbox providers like Yahoo) now require senders to adopt DMARC authentication. They are increasingly strict about unauthenticated email, especially from commonly spoofed domains. Your best defense against a sudden email rejection is to ensure all your emails are properly authenticated and aligned with a domain you own.
Resolving the 550-5.7.26 rejection
The explicit error message "550-5.7.26 Unauthenticated email from gmail.com is not accepted due to domain's DMARC policy" is definitive. It means Gmail's receiving servers have determined that the email is not genuinely from gmail.com because it failed DMARC authentication for that domain. This is not a transient issue; it's a policy enforcement.
This error can also appear if you're trying to send emails via a system (like a WordPress site or a CRM) that uses an @gmail.com "From" address but sends through its own mail server, or an unconfigured SMTP server. The solution remains the same: use a domain you own and ensure it's properly authenticated with SPF, DKIM, and DMARC. For more general DMARC issues, you can review common causes of DMARC verification failures.
DMARC policy (p=none)
Authentication (SPF/DKIM) for Sendgrid
Authentication (SPF/DKIM) for gmail.com
DMARC alignment
Gmail's action
p=none
Passes (for SendGrid)
Fails (not sent via Google's own servers)
Fails (From: gmail.com, authenticated by SendGrid)
Reject (internal policy for its own domain)
The path to proper email authentication
The most effective way to prevent these rejections and ensure reliable email deliverability is to stop using freemail domains (like gmail.com) as your "From" address when sending via an ESP. Instead, invest in and use a custom domain that you own and control. This allows you to set up proper email authentication, including SPF, DKIM, and DMARC, directly for your sending domain, ensuring alignment and improving your overall sender reputation.
For SendGrid users, this involves adding specific DNS records (usually CNAMEs) provided by SendGrid to your domain's DNS settings. Once these are in place, emails sent through SendGrid will be authenticated for your domain, achieving DMARC alignment and significantly reducing the likelihood of rejections or being marked as spam. Regularly monitoring your DMARC reports is also essential to catch any authentication issues early.
Own your domain: Purchase and use a dedicated domain for all your email sending.
Proper authentication: Configure SPF, DKIM, and DMARC records for your owned domain.
Align DMARC: Ensure your ESP's authentication aligns with your "From" domain.
Monitor DMARC reports: Regularly check your DMARC reports to identify and resolve issues.
Always use a domain you own for your 'From' addresses. This gives you full control over your email reputation and authentication.
Ensure SPF, DKIM, and DMARC are correctly configured for your owned sending domain.
Start DMARC policies at p=none to monitor, then transition to quarantine or reject as you gain confidence.
Common pitfalls
Using freemail domains (like gmail.com, yahoo.com) as your 'From' address for bulk or transactional mail via an ESP.
Assuming a p=none DMARC policy for a domain means emails failing authentication will never be rejected.
Neglecting to monitor DMARC reports, missing critical insights into email authentication issues.
Expert tips
Google and Yahoo are tightening authentication requirements for bulk senders. Proactive compliance is key.
Consider engaging a DMARC professional if you face complex authentication issues or manage high-volume sending.
A gradual rollout of stricter DMARC policies by mailbox providers is common to observe any unexpected issues.
Expert view
Expert from Email Geeks says that Gmail can implement any rules for incoming mail, especially when it impersonates their own domain, regardless of their public DMARC policy. Their public policy is merely a recommendation to other providers.
2023-07-27 - Email Geeks
Expert view
Expert from Email Geeks says that even before DMARC, it was common practice for domains to reject email claiming to be from their own domain but originating from external, unauthorized sources. This behavior is still valid and often implemented by large providers.
2023-07-27 - Email Geeks
Secure your email deliverability
The rejection of unauthenticated emails from gmail.com when sent via SendGrid or any other third-party ESP is a direct consequence of DMARC alignment failures and Gmail's stricter internal policies for its own domain. While gmail.com's public DMARC record might suggest otherwise, Google prioritizes protecting its users from spoofing and phishing attempts by rejecting such emails.
To ensure your emails reach the inbox, the definitive solution is to use a domain you own for your "From" addresses and properly configure SPF, DKIM, and DMARC for that domain. This approach not only resolves authentication failures but also builds a strong sending reputation, leading to better deliverability and trust with mailbox providers.
Gmail without Gmail's explicit authorization. SendGrid will correctly apply its own SPF and DKIM authentication to the email, but these will be for SendGrid's domain (e.g., sendgrid.net) or your verified sending domain, not gmail.com.
SendGrid, there's a misalignment because SendGrid's authentication doesn't match the "From" domain of gmail.com. This is why the email is flagged as "unauthenticated."
yahoo.com, or 
aol.com for bulk or transactional email via third-party services is generally considered a poor practice and a spam indicator. Major mailbox providers have taken steps to curb this behavior because it's a common tactic for phishing and impersonation. While SendGrid might still allow you to configure this, it often leads to deliverability issues, including emails being sent to spam or outright rejected.
SendGrid (or any ESP) to send on your behalf, DMARC alignment can be achieved. This means the authenticated domain matches your "From" domain.
