Create a Conditional Connector:

  1. Login to Office 365
  2.  Go to the “Admin Centers” > “Exchange
  3. Go to “Mail Flow” > “Connectors
  4. Press “+” to create a new connector and select the following
    From: Office 365
    To: Partner organization.
  5.  Press Next.
  6. Complete the “New Connector” as follows:
    Name: Enter a name for your connector
    Description: Enter a description (optional)
    Turn On: Select this option to enable the connector
  7. Press Next
  8. For “When to use Connector” select “Only when I have a transport rule setup that redirects messages to this connector“.
  9.  Press Next.
  10. For “How do you want to route email” select “Route email through these smart hosts
  11. Click the and enter the appropriate host name, then press Save.
             –  Acumen Zix Gateways:
    – zixgw01.csx1.net
    – zixgw02.csx1.net
  12. Press Next
  13.  Select the following options for “How should O365 connect to your partner”:
              Always use Transport Layer Security (TLS) to Secure the Connection (recommended)
    For Zix hosted mail systems, select: Issued by a trusted certificate authority (CA)

For on-site systems, select: Any digital certificate, including self-signed certificates
14. Click the Next button to verify your settings
15. Click the Next button to save the connector

16. The next screen will be used to validate the settings:
17. Press “+” to add an external email address
Add an email address of a recipient whose domain is external to your organization
18. Click the Validate button
19. Once Office 365 has been successfully validated, click the Save button

Create a Transport Rule to use The New Connector:

This transport rule helps to prevents mail loops and ensures only your company’s outbound emails (ie, not external emails sent to internal distribution lists) are routed to the connector

  1. Go to the “Admin Centers” > “Exchange
  2. Go to “Mail Flow” > “Rules
  3. Click the and select “Create new rule” from the drop down. This will open a new window.
  4. Click “More Options” at the bottom of the screen
  5. Give the rule a meaningful name
  6. Select the following options:

Under “Apply this rule if”
Select “The recipient…” > “is external/internal” -> “Outside the Organization“.

Under “Do the following”
Select “Modify the message properties” > “set a message header
Set the message header ‘routeto‘ to the value ‘zixserver

Under “Do the following”
Select “Modify the message properties” > “set a message header
Set the message header ‘routeto‘ to the value ‘zixserver
7. Press Add Action
8. Select “Redirect the Message to” -> “the following connector” -> (select the connector created above for Zix)

9. Under “Except if..”
10. Press Add Exception
Select “The sender..” > “is external/internal” -> “Outside of the organization
11. Press Add Exception

12. Select “A message header” > “includes any of these words” -> ‘routeto‘ header includes ‘zixserver
13. Press Save

  1. Open the rule and set the rule “Priority” to “0” (zero)
    15. Click Save

The rule should take effect within 5 – 15 minutes.

You may also wish to white list the Zix IP addresses.