Error code 550 due to Reject Direct Send feature in Microsoft Exchange

Disclaimer: This article is provided for instructional purposes only. To get more information in regards to these scenarios, we recommend to get in touch with the support team at Microsoft.

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

If you continue to experience the issues described in this article, consider one of these solutions:

Directly connect your non-Zendesk Microsoft Exchange-based email servers to your Zendesk Support instance using the Exchange Connector. This allows you to keep the Reject Direct Send setting enabled because with this setup, all email notifications are sent by your own Exchange server. Please note the limitations documented in the article on the Exchange Connector.

Instead of enabling the Reject Direct Setting, use a Transport rule to block, redirect or quarantine undesired emails, and exempt emails from Zendesk from the Rule, as described in the Microsoft FAQs. TheX-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.