Fix Xink Rerouting in Hybrid CMT Environments

Short answer:
In a hybrid Microsoft 365 setup with Centralized Mail Transport (CMT), Xink rerouting may bypass your on-premises Exchange. To fix this, create a connector and transport rule to route Xink-processed emails back through your on-premises environment.

This guide is intended for Exchange Administrators, IT Administrators, and Microsoft 365 Administrators.

Environment

Microsoft 365 and Exchange Server hybrid environment with Centralized Mail Transport (CMT) enabled.
All outbound emails from both on-premises and Exchange Online users are routed through the on-premises Exchange server.

Problem

After enabling Xink server-side (rerouting), outbound emails from Exchange Online users may be routed through Microsoft Exchange Online Protection (EOP) instead of your on-premises Exchange environment.

Solution

Ensure that Xink-processed emails are routed back through your on-premises Exchange by:

• Creating a new Outbound connector
• Creating a transport rule targeting Xink-handled messages

Step 1 – Create a new outbound connector

1. Sign in to the Microsoft 365 admin center.
2. Go to Mail flow > Connectors.
3. Create a new Outbound connector to route Xink-handled messages to your on-premises Exchange environment.

Step 2 – Create a transport rule for Xink-handled emails

Note: This rule must only apply to emails processed by Xink (identified by the header X-Xink-Handled).

1. In the Exchange Admin Center, go to Mail flow > Rules.
2. Click + and select Create a new rule.
3. Click More options to expand all settings.
4. Name the rule (e.g. FromXink-to-OnPremises).
5. Set the condition:
   A message header > includes any of these words
   Header name: X-Xink-Handled
   Value: Yes
6. Add action:
   Modify the message properties > set a message header
   Header: X-Goto-OnPremises
   Value: Yes
7. Add another action:
   Redirect the message to > the following connector
   Select your outbound connector (e.g. XinkOut-to-OnPremises)
8. Add an exception:
   A message header > includes any of these words
   Header: X-Goto-OnPremises
   Value: Yes
9. Click Save.

Result

All emails processed by Xink server-side will now be routed back to your on-premises Exchange environment.

Your Centralized Mail Transport configuration will then handle final delivery to recipients, ensuring consistent routing and compliance with your existing mail flow setup.