Log on to Office 365 Exchange Admin Center:
Click on Mail Flow.
Select Connectors and click the Plus icon, as shown below.
Select Office 365 in the From drop-down field, Partner organization from the To drop-down field, and click Next.
Enter a name for your connector, such as "Smart Host" or "SpamTitan", then click Next.
Select Only when email messages are sent to these domains, and click the Plus icon.
Enter a star / asterisk and click OK.
On the following screen, select Route email through these smart hosts and click the Plus icon.
Enter your smart host's hostname or IP address - e.g. cloud-out-c.spamtitan.com.
Repeat the above for each smart host and click Next when done.
Click Next on the following screen to accept the default TLS settings.
Click Next again to confirm.
To validate the connector, you need to enter an external email address (outside your organisation) to test the connection - e.g. firstname.lastname@example.org. To do this, click the Plus icon, enter the recipient address, and press OK.
Click Validate on the next screen.
It may take a minute for the validation to complete. You should see the following screen.
Once complete, you can close the confirmation and click Save.
Your connector should now be active and you can start routing your outbound mail through SpamTitan.