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

Disclaimer: This article is provided for instructional purposes only. For specific configuration assistance within Microsoft Exchange, please contact Microsoft Support.

Issue symptoms

Users within your company email domain are not receiving outgoing emails from your Zendesk account.

Email delivery failure notifications show the error: Recipient server rejected email. Status code: 550

Delivery logs show the specific error: 550 5.7.68 TenantInboundAttribution; Direct Send not allowed for this organization from unauthorized sources

Your organization uses Microsoft Exchange with the Reject Direct Send setting enabled.

These errors occur because your Microsoft Exchange security policies block emails from sender sources that are not explicitly authorized.

Resolution steps

Prerequisite: The following steps must be performed by your organization's Microsoft Exchange or Email Administrator.

Choose one of the following methods to allow Zendesk emails through your Exchange policy:

Option 1: Verify domain authentication (Recommended)

Ensure your external support address is fully authorized to send on behalf of your domain by setting up SPF, DKIM, and DMARC records.

Follow the instructions in Allowing Zendesk to send email on behalf of your email domain.

Option 2: Enable the Zendesk Exchange Connector

If you want to keep the Reject Direct Send setting enabled in Exchange without maintaining bypass rules, route your email directly through your own servers using the Exchange Connector.

Learn how to set this up in About the Microsoft Exchange connector.

Option 3: Create an Exchange Transport Rule bypass

If you prefer not to use the Exchange Connector, your email administrator can configure an Exchange Transport Rule to exempt Zendesk emails from being blocked by Direct Send rules.

In Microsoft Exchange Admin Center, navigate to Mail flow > Rules.

Create a rule that blocks or quarantines direct send emails, but add an exception for emails containing the header: X-Mailer: Zendesk Mailer

For full details on configuring Transport Rules, review the Microsoft Exchange FAQs.