IT Pro: Setup Hybrid mail flow to route through Exchange on-premises

This step-by-step guide is intended only for Exchange Administrator, IT Administrator, and Microsoft 365 Administrator.

Environment: 
Microsoft 365 and Exchange server Hybrid environment with Centralized Mail Transport(CMT) enabled.
All Outbound emails of On-prem and exchange online users must route through Exchange on-premise.

Problem:
Exchange online user's outbound emails are routed through Microsoft Online Protection(EOP) instead of through local exchange on-premises after you configure Xink server-side (Xink-rerouting).

Solution:
Configure Outbound and Xink handled emails to go through exchange on-premises by creating a new connector and a transport rule.


Step 1 - Create new Outbound Connector

1. Sign in to your Microsoft 365 admin center.
2. Go to Mail flow > connectors tab.
3. Create a new Outbound connector to route Xink-Handheld messages to exchange OnPrem (see image below)




Step 2 - Create a new transport rule that routes Xink-Handheld emails to Exchange on-prem environment.

Note: Since the problem is only affecting X-Xink-Handled messages then you must apply this new mail transport rule limited to X-Xink-Handled only.

1. In the Exchange admin center (Microsoft 365), go to mail flow > rules.
2. Click the + button and select Create a new rule.
3. Once the wizard opens, click More options (lower-left corner) to see all available settings.
4. Name your rule e.g 'FromXink-to-onPremises'
5. Select: A message header > includes any of these words > specify header name to X-Xink-Handled and the value to Yes.
6. Add the following action: Modify the message properties > set a message header to X-Goto-OnPremises and the value to Yes.
7. Click add action and choose: Redirect the message to > the following connector. Select the Outbound connector you previously created e.g 'XinkOut-to-on-Premises'.
8. Click add an exception to add the following exception: A message header > includes any of these words.
   Set the header name to X-Goto-OnPremises and the value to Yes. and Finally, click the Save button.
   
   
   Now all messages that are routed through Xink Server-side will be sent back to your local Exchange environment and Centralized Mail Transport configuration will send out the messages to its recipient.