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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: cURL error

Updated

By Duane GarnerChief Executive Officer (CEO)
Summarize: Claude ChatGPT View Markdown
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Your server could not complete the HTTPS request to an API mailer. The number after "cURL error" tells you whether it is DNS, connection or certificates.

Shown by every API mailer (Gmail, Microsoft 365, Amazon SES, SendLayer, SMTP.com, Brevo, SendGrid, Mailgun, Postmark, SparkPost, SMTP2GO, Mailjet, Elastic Email, MailerSend, Mandrill, Resend, Pepipost)

The test result or the error log shows cURL error followed by a number and a short reason, for example cURL error 7: Failed to connect or cURL error 60: SSL certificate problem.

This article is for site owners using an API mailer whose send fails before the service even answers.

What this error means

API mailers send your email as an HTTPS request from your web server to the service. WordPress uses a library called cURL for that. A cURL error means the request never completed: the server could not find the service, could not connect, or could not set up a secure connection. The mail service has not seen your message, so your key and settings have not been checked yet.

The number is the useful part:

cURL error What it means
6 The service's name could not be looked up (DNS).
7 The server could not connect to the service.
28 The request timed out. See the timeout article.
35 The secure (TLS) handshake failed.
60 The service's certificate could not be checked against trusted authorities.
77 The server's certificate bundle file could not be read. See the cURL 77 article.

Common causes

  • Your web host blocks outgoing HTTPS connections, or only to certain addresses.
  • The server's DNS resolver is not working.
  • The server's OpenSSL, cURL or CA certificate bundle is out of date, so modern certificates or TLS versions fail.
  • A firewall or security plugin on the server filters outgoing requests.
  • A proxy is required on the server and WordPress is not set up to use it.
  • A short outage at the mail service or on the network.

How to fix

  1. Note the number

    Open the error with View Error Log in the failed-send banner, or in CRM-NG SMTP → Tools → Debug Events, and match the number to the table above.

  2. Check the service's status

    Look at the mail service's status page for an outage.

  3. Check your settings

    Go to CRM-NG SMTP → Settings → General and confirm the Mailer and, where present, Region are right. A wrong region sends the request to a different address.

  4. Ask your web host

    Ask them to confirm the server can make outbound HTTPS requests to the mail service, that DNS works, and that OpenSSL, cURL and the CA bundle are current. Share the full error.

  5. Send a test

    Go to CRM-NG SMTP → Tools → Email Test, fill in Send To and press Send Email.

Verify it worked

The test page shows "Test email sent successfully! Check your inbox to confirm delivery." If the error changes to a 401 or a key message, the connection works and you can fix the credentials next.

Notes

  • If other plugins also fail to reach outside services (updates, licence checks), the problem is the server, not CRM-NG SMTP.
  • WordPress Tools → Site Health shows whether the site can make loopback and outbound requests.
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