Issue symptoms

  • Users within your company's email domain do not receive outgoing emails from your Zendesk account.
  • Email delivery failure notifications to those recipients include an error of Recipient server rejected email. Status code: 550
  • Delivery logs show a more specific error of 550 5.7.68 TenantInboundAttribution; Direct Send not allowed for this organization from unauthorized sources.
  • Your organization has the Reject Direct Send feature enabled in Microsoft Exchange.

These errors occur because your organization's Exchange policies are actively blocking emails from reaching their intended recipients. This happens when Zendesk isn’t recognized as an authorized sender for your external support address.

Resolution steps

These errors originate from Microsoft, not Zendesk. Your email administrator is responsible for reviewing the error message and verifying your email configuration. However, Zendesk offers basic guidance to help you set up your external email address successfully.

To resolve outgoing email delivery issues, ensure your external support address is properly configured and meets all setup requirements:

  • Allowing Zendesk to send email on behalf of your email domain
  • Updates to Microsoft sender requirements

If your organization needs to keep the Reject Direct Send setting enabled, you can authorize Zendesk as a sender using one of the following methods:

  • Directly connect your non-Zendesk Microsoft Exchange-based email servers to your Zendesk Support instance using the Exchange Connector.
  • Use a Transport rule to exempt emails from Zendesk from being blocked by the Reject Direct Send setting, as described in the Microsoft FAQs. The X-Mailer: Zendesk Mailer header may be used to identify mail sent from Zendesk. Your email administrator is responsible for completing this setup, and Zendesk Support cannot provide guidance on its specific configuration.
  • Add Zendesk’s IP ranges to your SPF record. You can find the current IP ranges used by Zendesk’s mail servers by following the instructions in the article: Configuring your firewall for use with Zendesk. Keep in mind that these IP ranges may change without prior notice, so this method requires regular monitoring and updates to maintain email deliverability
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