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✉️ Email Delivery

Documentation, reference material and tutorials for CRM-NG SMTP Email: setup guides for every mail service, troubleshooting, and one article per error message.

Error: Unauthenticated (MailerSend)

Updated

By Duane GarnerChief Executive Officer (CEO)
Summarize: Claude ChatGPT View Markdown
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MailerSend refused the request because the API key CRM-NG SMTP sent is missing, wrong or deleted. Create a fresh key and paste it in.

Shown by the MailerSend mailer

The test result, the failed-send banner or Tools → Debug Events shows a message such as Unauthenticated. (often with HTTP status 401) after CRM-NG SMTP tries to send through MailerSend.

This article is for site owners who use the MailerSend mailer and see this message on a test email or in the error log.

What this error means

Every request CRM-NG SMTP makes to MailerSend carries your API key. MailerSend checks that key before it looks at anything else in the message. "Unauthenticated" means the check failed: MailerSend could not match the key to an active token on any account, so it rejected the request without trying to send.

Nothing is wrong with your message, your recipients or your domain at this point. The problem is only the key.

Common causes

  • The API Key field is empty, or the key was pasted with a missing character, a leading or trailing space, or a line break.
  • The token was deleted or regenerated in MailerSend after you saved it in CRM-NG SMTP.
  • The key belongs to a different MailerSend account than the one where your domain is set up, and that account has since been closed.
  • The key was copied from somewhere other than MailerSend's token screen, for example an SMTP password for the same account.
  • The key is set in wp-config.php with a CRMNG_SMTP_* constant, and the constant still holds an old value.

How to fix

  1. Sign in to MailerSend

    Open https://app.mailersend.com/ with the account that owns your sending domain.

  2. Open the API tokens page

    Go to Integrations and choose API tokens (MailerSend also links to it from each domain's settings page). Look for the token you used for this site.

  3. Create a new token

    Choose to generate a new token, give it a name such as the site's address, and pick the domain it may send from. Give it at least sending access for email; full access is not needed.

  4. Copy the token once

    MailerSend shows the full token only at creation. Copy it straight away, without spaces.

  5. Replace the key in CRM-NG SMTP

    Go to CRM-NG SMTP → Settings → General. Check that Mailer is set to MailerSend. If a key is already stored, press Remove API Key, then paste the new token into API Key.

  6. Save

    Save the settings and wait for "Settings were successfully saved."

  7. Send a test

    Go to CRM-NG SMTP → Tools → Email Test, enter your own address in Send To and press Send Email.

Verify it worked

The test page shows "Test email sent successfully! Check your inbox to confirm delivery." and the message arrives. In MailerSend, the activity page for your domain lists the test email. The failed-send banner disappears after the next successful send.

Notes

  • If the API Key field is greyed out, the key is fixed in wp-config.php. Change the constant there instead. See secure settings with constants.
  • Delete the old token in MailerSend once the new one works, so a leaked copy cannot be used.
  • If the error changes to a message about your domain or a trial account, the key is now accepted and you have moved on to the next step. See the related articles below.
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