Internal routing causes email delivery failure to domains not on Email Security.cloud

Products

• Email Security.cloud

Issue/Introduction

Emails sent to a specific recipient are not received, even though colleagues receive mail from the same sender successfully. Track and Trace logs may show no record of the specific failure because the mail is being routed internally before reaching the service.

Environment

Email Security.cloud

Cause

Internal forwarding rules, aliases, or Transport Rules within the customer's mail environment (e.g., Exchange/Office 365) are redirecting the email to a different domain. If this redirected domain is not pointing to Email Security.cloud, the message will not appear in the service logs and may fail delivery.

Resolution

1.  Identify the exact recipient address being used at the time of delivery failure from the internal mail server logs.
2.  Check for internal forwarding rules, aliases, or Transport Rules for the affected mailbox.
3.  Verify if any redirection to an internal domain (e.g., ####@####.com) is occurring.
4.  Confirm the redirected domain is correctly configured to point to Email Security.cloud if filtering is required.
5.  Disable or update any incorrect redirection rules to ensure mail follows the expected external MX record path.