Do these steps to create a rule in Microsoft Exchange On-premise:

1. Go to the Exchange Admin Center (EAC).
2. Log in to the EAC as an administrator.
3. Go to Mail flow in the menu on the left.
4. Go to Rules.
5. Click the add button.
6. Click Create a new rule....
7. Give the rule a name.
   For example: Zivver Encryption Gateway.
8. At the bottom, click More options....
9. Under *Apply this rule if..., select The subject or body... and then subject includes any of these words.
10. Add a word or phrase.
    For example: Secure.
    
    Tip

    You can include the regex (?i) to make the check case-insensitive.
    For example: (?i)Secure.
11. Click the add button.
12. Click OK.
13. Under *Do the following..., select Redirect the message to... and then these recipients.
14. Look up the contact that was created previously and select it.
15. Click Add ->.
16. Click OK.
17. Under Except if..., click add exception.
18. Select A message header... and then matches these text patterns.
19. Click on *Enter text....
20. Enter X-Zivver-Transport.
21. Click OK.
22. Click *Enter text patterns....
23. Enter ..*. (That is 2 dots, 1 asterisk/wildcard, 1 dot).
24. Click the add button.
25. Click OK.
26. Under Choose a mode for this rule, select Enforce.
27. Enable the option Defer the message if rule processing doesn’t complete.
    If you enable this option, a message will not leave Exchange until it has been checked by this rule. If for any reason Exchange temporarily does not check messages for this rule, processing of those messages will be paused.
28. Click Save.

The mail flow rule is now set. Please ensure that the priority of all existing rules is correct. If the sent message needs to be processed by other rules first, make sure that the rule created for the Encryption Gateway has a lower priority.

Any outbound message that matches the filter will be submitted to the Zivver SMTP Server. If this is not desired, please deactivate the rule.