---
title: "How to fix the 550 5.7.26 unauthenticated sender error in Gmail? | DuoCircle"
description: "How to fix the 550 5.7.26 unauthenticated sender error in Gmail?"
image: "https://www.duocircle.com/images/og-default.png"
canonical: "https://www.duocircle.com/blog/email-security/how-to-fix-the-550-5-7-26-unauthenticated-sender-error-in-gmail/"
---

Quick Answer

The "550 5.7.26 This Mail is Unauthenticated" error from Gmail means your domain failed Google's authentication checks under the bulk-sender requirements that took effect in February 2024\. For senders under 5,000 messages a day, common causes include missing SPF or DKIM, a spam complaint rate above 0.3%, no TLS connection, missing ARC for forwarded mail, or broken forward and reverse DNS. For senders over 5,000 a day, all three of SPF, DKIM, and DMARC are mandatory, with the From domain aligning to either SPF or DKIM, and a one-click List-Unsubscribe header on marketing mail. Fix it by publishing valid SPF and DKIM records, adding a DMARC record at \_dmarc starting at p=none, ensuring the From header aligns with the authenticated domain, and keeping spam rate under 0.1% (with 0.3% as the hard ceiling).

How to fix the 550 5.7.26 unauthenticated sender error in Gmail?

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![DMARC](https://media.mailhop.org/duocircle/images/2024/06/what-is-dkim-4.jpg) 

Back in October 2023, Google released its revamped version of [email-sending policies](https://blog.google/products/gmail/gmail-security-authentication-spam-protection/), which **mandated bulk email senders** to comply with the new authentication standards by February 2024\. Cut to today: Google has now officially started rolling out these updated policies, and some organizations are receiving the following **error message** while sending emails:

`_“gmail-smtp-in.l.google.COM: 550-5.7.26 This mail has been blocked because the sender is unauthenticated.”_`

Have you been facing the same issue? The reason you’re receiving this message is that your **domain isn’t properly authenticated**. _According to the updated [policy by Google](/email-services/google-yahoo-mandatory-to-deploy-dmarc-for-more-than-5000-daily-emails/), if your organization sends out more than 5,000 emails per day, it must be authenticated with **SPF, DKIM, and DMARC**_.

Let’s decode this error message and **learn how we can fix it** to ensure a seamless and efficient [email delivery](https://www.bleepingcomputer.com/news/technology/att-delays-microsoft-365-email-delivery-due-to-spam-wave/).

[![Email Deliverability](https://media.mailhop.org/duocircle/images/2024/06/what-is-DKIM-1.jpg)](https://media.mailhop.org/duocircle/images/2024/06/what-is-DKIM-1.jpg)

## What Does the “550 5.7.26 This Mail is Unauthenticated” Error Mean?

If your emails are being **blocked by Gmail** and you’re receiving an error message that says “550 5.7.26 This Mail is Unauthenticated,” it is a clear sign that your domain isn’t authenticated **as per Google’s** [latest updates](https://blog.google/products/search/google-search-update-march-2024/).

As you know, the new policy updates require you to authenticate your outgoing emails; when you send out an email, Gmail checks if and how well your email domain is authenticated. If Gmail finds that your email lacks proper authentication, it **will block the email** to protect recipients from potential spam and [phishing attacks](https://coinfomania.com/phishing-attacks-on-the-rise-in-ton-ecosystem/).

Apart from this, **there are other reasons** why this error message might appear when you send emails. However, it is important to understand that these reasons might differ according to your [email-sending practices](https://depaul.service-now.com/sp/en/email-best-practices-for-sending-to-many-recipients?id=kb%5Farticle%5Fview&sysparm%5Farticle=KB0010584). Let us take a look at them:

### If You Send Less Than 5,000 Emails Per Day

- Your [email-sending domain](https://foghornlabs.com/email-sending-domains-your-brands-digital-address/) is **not authenticated** with either SPF or DKIM
- Your [email spam rate](https://emailmastery.org/email-marketing-glossary/spam-rate/) is **above 0.3%**
- _Your Gmail From: headers are being impersonated_
- You’re not utilizing a [TLS connection](https://en.wikipedia.org/wiki/Transport%5FLayer%5FSecurity) for sending emails
- Your domain **does not have** the [Authenticated Received Chain (ARC)](https://proton.me/blog/what-is-authenticated-received-chain-arc) enabled for forwarded emails
- _There are errors in your forward and reverse [DNS records](/data-privacy/dns-record-types-defined-and-explained/)_

### If You Send More Than 5,000 Emails Per Day

- You do not have SPF and [DKIM](/resources/what-is-dkim) implemented for your domain
- Your domain is **not authenticated with DMARC**
- Your sender [mimics Gmail From: headers](https://7news.com.au/news/cyber-security/google-warns-of-gmail-tech-support-impersonation-scam-c-11196287)
- You are not using a TLS connection to transmit emails
- **ARC is not enabled** for forwarded messages
- Your forward and reverse DNS records are invalid
- You do not offer [easy unsubscribe](https://www.theverge.com/2024/1/20/24044923/google-is-making-it-easier-to-unsubscribe-to-emails) from your marketing messages to your recipients

### Other Reasons Why You Are Receiving the Error Message

- Your messages include **spammy or inappropriate content**
- You have a poor [sender reputation](/resources/email-sender-reputation) among recipients, your emails have been reported by them
- Your **domain/IP has been blocklisted**
- You’re sending emails to the [wrong target audience](https://fastercapital.com/content/The-dangers-of-not-targeting-a-specific-market.html); that is, these **emails don’t align with their interests** and end up falling into the spam folders

[![email marketing](https://media.mailhop.org/duocircle/images/2024/06/smtp-server-mail-5137.jpg)](https://media.mailhop.org/duocircle/images/2024/06/smtp-server-mail-5137.jpg)

## How Do You Know if Gmail is Blocking Your Emails?

You might be crafting the most immaculate emails for your audience, but if your domain does not comply with Google’s new email-sending policies, all your [email marketing](/email-services/5-common-email-marketing-challenges-and-how-to-overcome-them/) efforts might go in vain. Before addressing this issue, let’s first understand **how to determine if Gmail is blocking** your emails.

The first and the most obvious sign that your emails are being rejected by Gmail is receiving **bounce-back messages** with error code 550-5.7.26\. You might also notice a sudden drop in the [engagement rates](https://sproutsocial.com/glossary/engagement-rate/) of your emails. That is to say, they are not being as well received by the recipients or are being **filtered into spam folders** instead of reaching the inboxes.

## How to Fix the “550 5.7.26 This Mail is Unauthenticated” Error?

Now that we have figured out the reasons behind the “550 5.7.26 This Mail is Unauthenticated” error message, it is time to **learn how to fix** the issue. Here’s how you can do it:

### Implement Sender Policy Framework (SPF)

_To fix the unauthenticated sender error in Gmail, you should start by implementing [SPF](/content/spf-record-check)._ By specifying which **mail servers** are authorized to send emails on behalf of your domain, you can prevent [unauthorized users](https://www.yahoo.com/news/ticketmaster-notifies-users-unauthorized-activity-233104470.html) from sending emails that appear to come from your domain, which is one of the primary concerns of email service providers. 

### Set up DomainKeys Identified Mail (DKIM)

The next step towards achieving compliance is to **enforce DKIM**, which helps verify that the contents of your emails have not been altered in transit and confirms that they were sent from your domain. This simple step reinforces the trustworthiness of your emails and improves their [email deliverability](/a-guide-on-email-deliverability).

### Employ Domain-based Message Authentication, Reporting, and Conformance (DMARC)

Perhaps the most important step of them all, implementing [DMARC](/email/dmarc), is crucial for providing **instructions to receiving mail servers** on how to handle emails that fail SPF or [DKIM checks](/email-security/canonicalization-reason-behind-dkim-signature-verification-failures/). One of the main reasons that Google has made it mandatory for organizations that send bulk emails to authenticate their domains with DMARC is because this authentication protocol helps **build a strong defense** against phishing and [email spoofing](https://techcrunch.com/2024/06/18/security-bug-allows-anyone-to-spoof-microsoft-employee-emails/) by specifying policies for handling unverified emails. 

### Offer Unsubscribe Option to Your Recipients

An important update in Google’s revamped email-sending policies is that your [marketing emails](https://www.forbes.com/advisor/business/software/best-time-send-marketing-emails/#which%5Fis%5Fthe%5Fbest%5Fday%5Fto%5Fsend%5Fmarketing%5Femails%5Fsection) **must include an unsubscribe button** so that recipients can easily opt out of receiving the emails they no longer require. 

### Stay Up-to-date with Best Practices

_Email service providers like Google and Yahoo keep updating their policies regularly to **enhance security** and combat spam._ To ensure that you are way ahead of the [cyber attackers](https://www.bbc.com/news/articles/c9777v4m8zdo) and that your emails seamlessly reach the intended recipients’ inboxes, you should regularly review and adjust your email sending practices as per the **latest guidelines and industry trends**. 

Need help fixing the “550 5.7.26 This Mail is Unauthenticated” issue? Our team at [DuoCircle](/) has got you covered! From implementing SPF, DKIM, and DMARC to regularly monitoring email delivery issues, we provide comprehensive solutions to ensure that your emails are **properly authenticated** and delivered. [Contact us today](/contact) to resolve your [email authentication](/resources/email-authentication) issues and optimize your email marketing efforts.

## Topics

email securityUpdates 

![Brad Slavin](https://media.mailhop.org/dmarcreport/images/team/brad-slavin.jpg) 

Brad Slavin 

General Manager

General Manager at DuoCircle. Product strategy and commercial lead across the email security portfolio.

## Secure your email infrastructure

Protect, authenticate, and deliver. Contact our team to find the right solution.

[Contact Sales](/contact/) [Explore Products](/products/) 

## Related Articles

[  Email Security 7m  10 Crucial Tips that Will Help You Avoid Spam Filters and Send Better Emails  Feb 14, 2023 ](/blog/email-security/10-crucial-tips-that-will-help-you-avoid-spam-filters-and-send-better-emails/)[  Email Security 6m  5 Reasons Why Your Website Needs an SPF Record Flattener?  Sep 26, 2023 ](/blog/email-security/5-reasons-why-your-website-needs-an-spf-record-flattener/)[  Email Security 8m  Best Practices to Follow When Implementing SPF, DKIM, and DMARC  Mar 19, 2024 ](/blog/email-security/best-practices-to-follow-when-implementing-spf-dkim-and-dmarc/)[  Email Security 3m  Best Ways to Secure Emails in 2024  Apr 26, 2024 ](/blog/email-security/best-ways-to-secure-emails-in-2024/)

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