SMTP Error 521: Server Does Not Accept Mail

Overview

‘Error 521: Server does not accept mail’ indicates that a mail server isn’t set up to accept incoming emails. It often occurs in mail relay situations where servers act as intermediaries in the email delivery process.

Causes

This error is often related to mail relay servers. Below, we’ve highlighted the main causes of the error.

  1. Mail relay configuration: The server is configured to pass emails along in the relay chain rather than handling final delivery.
  2. Server misconfiguration: The recipient’s mail server may not be properly set up to accept incoming emails.

In simple terms, when you encounter this error, the server is saying it’s passing the email along in the relay chain, but it isn’t its final destination.

Solution

To address the ‘SMTP error 521’ issue, first check if the emails have actually been successfully relayed and delivered to the intended recipients. ThisĀ error doesn’t always mean the email wasn’t delivered.

If the email recipients confirm they haven’t received the email, you’ll need to pinpoint the exact relay that is affected. This typically involves reachingĀ out to the administrators of the recipient’s mail server.

That’s it! Now you know the common causes of the 521 error and how to resolve it.

Would you like to explore other email service providers WP Mail SMTP supports? Be sure to check our complete guide to WP Mail SMTP mailers.