What does 'Authenticated user is not authorized to send mail' mean when using GSuite API?
Matthew Whittaker
Co-founder & CTO, Suped
Published 13 May 2025
Updated 19 Aug 2025
6 min read
When you're working with the Google Workspace (formerly GSuite) API and encounter the error "Authenticated user is not authorized to send mail", it can be a frustrating experience. This message indicates that while your application successfully authenticated itself with Google, the specific account or service trying to send the email lacks the necessary permissions (authorization) to perform that action.
This isn't an issue with your email authentication protocols like SPF, DKIM, or DMARC. Those are about verifying your domain's legitimacy to receiving servers. Instead, this error points to a problem within the Google environment itself, specifically with the permissions granted to the identity making the API call.
It means the API request was rejected because the authenticated identity simply doesn't have the authority to send emails from the specified account or domain. Let's delve into why this happens and how to resolve it.
Understanding the API error message
The error message Authenticated user is not authorized to send mail often comes with a HTTP 401 Unauthorized status code. While 401 typically means authentication failed, in the context of Google's API, it sometimes means that while the credentials were valid, the authenticated identity is not permitted to perform the requested action. This is more akin to a 403 Forbidden error, which signifies a lack of authorization despite successful authentication.
This distinction is crucial for troubleshooting. If it were purely an authentication failure, the message would likely be about invalid credentials or tokens. Instead, it clearly states that the authenticated user is the problem, not the authentication process itself.
API response codes explained
401 Unauthorized: This indicates that the request lacks valid authentication credentials for the target resource. While Google may return it for authorization issues, it fundamentally means access is denied based on who you are (or are perceived to be).
403 Forbidden: This response means the server understood the request but refuses to authorize it. This often means the authenticated user (or service account) does not have the necessary permissions to access the resource or perform the action. In many cases, the Authenticated user is not authorized to send mail error aligns more closely with a 403 scenario.
Common causes of authorization failures
Several factors can lead to this authorization issue, ranging from misconfigured permissions to policy violations. Understanding the common culprits helps in quickly identifying and rectifying the problem.
One of the most frequent reasons is that the Google Workspace user or service account attempting to send email does not have the necessary Gmail API scopes enabled or granted within Google Cloud Platform. Each API operation requires specific permissions, and sending mail is no exception. If the account isn't explicitly granted the https://www.googleapis.com/auth/gmail.send scope, it won't be authorized.
Another common cause, particularly when using service accounts to send on behalf of users, is incorrect or missing domain-wide delegation. This feature allows a service account to impersonate users in your Google Workspace domain to access user data without requiring direct user consent. If this isn't configured correctly, the service account won't have the authority to send emails as those users.
User accounts
Gmail user accounts are typically used for direct human interaction and require OAuth 2.0 consent from the user.
Setup: Requires user interaction to authorize your application's access via a web flow. The user grants specific permissions (scopes) to your app.
Permissions: Access is tied to the individual user's permissions within their Google Workspace account. If the user account itself is suspended or doesn't have sending rights, the API call will fail.
Use cases: Applications that send emails on behalf of a specific user, like a CRM or customer support tool.
Service accounts
Service accounts are special types of Google accounts used by applications to interact with APIs. They do not represent a human user.
Setup: Authenticated using a private key file. To send emails on behalf of users, they require domain-wide delegation configured in the Google Workspace Admin console.
Permissions: Determined by the scopes granted to the service account and the permissions of the impersonated user.
Use cases: Automated tasks, background services, or applications managing users across an entire Google Workspace domain.
Finally, policy violations are a significant reason for this error. If Google detects that the account is being used for spamming, sending unsolicited bulk emails, or any other activity that violates their acceptable use policies, they may revoke the account's ability to send mail via the API. This is a common measure to combat abuse.
Troubleshooting steps for API authorization
Troubleshooting this error requires a systematic approach, checking various settings within your Google Cloud project and Google Workspace Admin console. It's often not an email deliverability problem in the traditional sense, but rather a configuration issue with your API access.
First, verify the API scopes you are requesting. For sending emails through Gmail API, you typically need the https://www.googleapis.com/auth/gmail.send scope. Ensure this is explicitly requested in your application's code during the OAuth 2.0 flow or when setting up domain-wide delegation for service accounts.
For service accounts, check the Google Workspace Admin console under Security > Access and data control > API Controls. Ensure that Domain-wide delegation is properly configured with the correct client ID of your service account and the required OAuth scopes. If you're encountering this specific authorization error, it's often an indicator that the user whose email you're trying to send via the API (or the service account itself if sending as the service account email) either has Gmail disabled or has been suspended for sending.
If all technical configurations seem correct, the issue might stem from a policy violation or account suspension. Google has strict policies against spamming and may revoke sending privileges if they detect suspicious activity. In such cases, checking the Google Postmaster Tools for your domain's reputation and potential issues is a good next step. You might also need to contact Google Workspace Support directly, providing the exact error message and correlation ID.
Preventative measures and policy adherence
Preventing the Authenticated user is not authorized to send mail error often comes down to careful configuration and adherence to Google's policies. Always ensure that the Google Cloud project and Google Workspace settings align with the intended use of the Gmail API.
Regularly review your API key usage and SMTP relay configurations to ensure they are up-to-date and compliant. Avoid sending large volumes of unsolicited emails, as this is a primary trigger for account suspensions and blacklist (or blocklist) entries. If you're using a third-party service or WordPress plugin to send emails via the GSuite API, confirm their practices align with Google's guidelines. Some third-party tools, even if seemingly benign, can misuse API access, leading to these authorization blocks without your explicit knowledge.
Beware of unapproved sending practices
Google is very sensitive to email sending practices that deviate from typical user behavior. If your application or a third-party service connected to your GSuite API is sending emails that appear to be unsolicited, promotional, or high-volume without proper opt-in, Google's automated systems may flag your account. This can result in your Google Workspace account being suspended from sending mail via the API, even if other forms of email sending (like through the Gmail web interface) remain active.
Views from the trenches
Best practices
Always use the principle of least privilege when granting API scopes to avoid over-permissioning.
Regularly audit your Google Cloud project's API credentials and service account permissions.
Implement robust logging for your email sending application to capture detailed API responses.
Monitor your Google Postmaster Tools for any reputation warnings or spam rate increases.
Common pitfalls
Using a service account without proper domain-wide delegation for impersonation.
Requesting insufficient (or incorrect) API scopes for email sending operations.
Ignoring Google's warnings about suspicious email activity, leading to suspension.
Assuming general email authentication (SPF/DKIM/DMARC) covers API authorization.
Expert tips
Confirm that the specific user account being impersonated by a service account still has active Gmail service enabled within Google Workspace.
If migrating or setting up new services, test API sending with a small volume before full deployment.
For unexpected 401/403 errors, double-check that the API key or service account credential hasn't been revoked or expired.
Be cautious with WordPress plugins that send email, as some might not follow best practices or could be compromised.
Expert view
Expert from Email Geeks says this message is definitively an API response. While it's a 401 code, it functions more like a 403, indicating that the authenticated user is recognized but not authorized to send mail through the API endpoint.
2023-12-01 - Email Geeks
Expert view
Expert from Email Geeks says the user has successfully logged in to the API, but the specific user identity they've logged in as simply lacks the permission to send email.
2023-12-01 - Email Geeks
Key takeaways
The "Authenticated user is not authorized to send mail" error from the GSuite API is a clear signal that, while your application's identity is verified, its permissions to send emails are not in order. Resolving this primarily involves reviewing and correctly configuring API scopes, service account delegation, or direct user permissions within your Google Cloud project and Google Workspace Admin console. It's also a strong indicator to review your email sending practices to ensure they comply with Google's policies and avoid any activities that could lead to suspension or being blacklisted.
Gmail user accounts are typically used for direct human interaction and require OAuth 2.0 consent from the user.
Google Workspace account. If the user account itself is suspended or doesn't have sending rights, the API call will fail.
