Create your first rule
In this guide you will create a policy rule that prepends [EXTERNAL] to the subject of emails sent from a specific address. This is a common practice that helps recipients instantly recognize messages from outside the organization.
Using a single test sender address means no additional configuration is required - and the rule will only affect messages from that address, so you can verify everything works before broadening it to production use.
What you will build
| Setting | Value |
|---|---|
| Rule type | Policy rule |
| Condition | Message Sender = your test address |
| Action | Modify Subject - prepend [EXTERNAL] |
Step 1 - Open Policy Rules and create a new group
In the Administrator Panel, navigate to Policy Rules.
Click Add group, enter a name such as My first rules, and save it.
Groups act as folders for related rules - this keeps things organized as you add more rules later.
Step 2 - Add a rule to the group
Open the group you just created and click Add rule.
Step 3 - Add the Message Sender condition
In the rule editor, go to the Conditions tab and click Add condition. Select Message Sender.
Enter the email address of your test account - for example tester@gmail.com - and set the match type to Exact match.
The rule will only match messages sent from that specific address, so real mail from other senders remains completely unaffected during testing.
Step 4 - Add the Modify Subject action
Go to the Actions tab and click Add action. Select Modify Subject.
Choose Use the original subject and prepend text to it and enter [EXTERNAL] as the text to prepend (note the trailing space).
| Example | |
|---|---|
| Subject before | Meeting follow-up |
| Subject after | [EXTERNAL] Meeting follow-up |
Step 5 - Name and save the rule
Go to the Name tab, enter a descriptive name such as Tag external emails, and save the rule.
Make sure the rule and its group are both marked as active.
Step 6 - Verify with Rules Tester
Before sending any real email, use the built-in Rules Tester to confirm the rule behaves as expected.
Navigate to Rules Tester in the Administrator Panel and compose a test message:
- From - the test address you entered in Step 3 (e.g.
tester@gmail.com) - To - any address inside your organization
- Subject - any subject, e.g.
Meeting follow-up
Click Send. In the results you should see the rule matched and the subject changed to [EXTERNAL] Meeting follow-up.
If you change the From to any other address, the rule should not match - confirming the sender restriction works correctly.
Next steps
Once you are happy with the behavior, you can broaden the rule for production use. Replace the exact address with a wildcard like *@gmail.com to match an entire domain, or remove the Message Sender condition entirely to tag all incoming messages regardless of sender.
For even more precise control, you can also add a Message Direction condition set to Incoming - this targets only messages arriving from outside your organization. That condition requires Directory Service to be configured first.
Additional resources
- Message sender - filter messages based on the sender's email address, domain, or group
- Message direction - filter messages based on whether they are incoming, outgoing, or internal
- Modify subject - prepend, append, or replace the subject line of a message