How to Add External Email Warning and Tag to Office 365 and Outlook

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In today’s digital world, security threats such as phishing and email scams are increasing rapidly. Adding an external email warning in Office 365 and Outlook helps users identify emails coming from outside the organization. This simple yet effective security measure can prevent employees from clicking on malicious links or sharing sensitive information with unauthorized individuals.

This guide will walk you through the process of adding an external email warning and tagging external emails in Office 365 and Outlook. The instructions are user-friendly and easy to follow, even for beginners.

Why Should You Add an External Email Warning in Office 365 and Outlook?

1. Improves Security

By marking external emails with a warning, users can quickly identify messages from outside sources and avoid potential security risks.

2. Prevents Phishing Attacks

Hackers often disguise emails to appear as if they are from someone within the organization. Adding an external email warning can help prevent users from falling for phishing attempts.

3. Enhances User Awareness

Employees become more cautious when they see an external tag, reducing the chances of accidental clicks on harmful links.

4. Reduces Human Errors

Since many cyberattacks rely on human mistakes, a warning message can serve as a reminder to double-check the sender’s email address before responding.

Prerequisites for Configuring External Email Warning in Office 365

Before adding a External Email Warning to your Office 365 or Outlook, make sure you meet the following prerequisites:

Administrator Access: You need to have administrator access to your Office 365 or Microsoft 365 account.
Exchange Online: Ensure that Exchange Online is part of your Microsoft 365 subscription.
Exchange Admin Center (EAC): You will need access to the Exchange Admin Center (EAC) to configure mail flow rules for External Email Warning.

Step-by-Step Guide to Add an External Email Warning in Office 365

Follow these steps to enable external email tagging in Office 365.

Step 1: Sign in to Microsoft 365 Admin Center

Open your web browser and go to the Microsoft 365 Admin Center.
Log in using your admin credentials.

Step 2: Access Exchange Admin Center

In the left-hand menu, click on Exchange to open the Exchange Admin Center (EAC).
Click on Mail Flow from the left menu.
Select Rules to create a new mail rule.

Step 3: Create a New Mail Rule

Click on + Add a Rule.
Choose Create a New Rule.
Enter a name such as External Email Warning.

Step 4: Configure the Rule Conditions

Under “Apply this rule if,” select The sender is located…
Choose Outside the organization.
Under “Do the following,” select Prepend the subject of the message with…

Enter a warning message such as:

[External Email] Be cautious before clicking links or opening attachments.

Step 5: Save and Apply the Rule

Click Save to activate the rule.
The rule will now be applied to all incoming external emails.

How to Add an External Email Warning in Outlook

If you want to add a warning message directly in Microsoft Outlook, follow these steps:

Step 1: Open Outlook and Access Rules

Open Microsoft Outlook.
Click on File > Manage Rules & Alerts.
Click New Rule.

Step 2: Set Up a New Rule

Select Apply rule on messages I receive.
Click Next and check from people or public group.
Click on Specified, then enter external email domains (e.g., @gmail.com, @yahoo.com).

Step 3: Apply an Action

Choose display a specific message in the New Item Alert Window.

Enter a custom warning message like:

Caution: This email is from an external sender. Verify before opening.

Click Finish to activate the rule.

Best Practices for External Email Warning in Office 365 and Outlook

1. Use Clear and Simple Warnings

Ensure the external email warning message is easy to read and understand.

2. Avoid Overloading Users

Do not use excessive warnings that may be ignored over time.

3. Regularly Review Email Rules

Monitor and update rules periodically to maintain security effectiveness.

4. Train Employees on Email Security

Educate staff on how to recognize phishing attempts and external email risks.

Testing the External Email Warning

Once you have configured the External Email Warning, it’s crucial to test it. Here’s how you can do that:

Send a test email from an external email account (not within your domain).
Check the recipient’s inbox to ensure the warning or tag is visible on the email.
Confirm that the subject is updated with the warning, and if configured, the body of the email displays the custom warning message.

Avoiding False Positives for Some Friendly Domains

Sometimes, your organization may regularly communicate with trusted external vendors, partners, or clients. In such cases, these emails should not trigger the External Email Warning.

To avoid false positives, follow these steps:

Create a Safe List:
- In the Exchange Admin Center, under Mail Flow, you can create exceptions for specific domains or email addresses that should not be flagged as external emails.
Set Up Mail Flow Rule Exceptions:
- When configuring the mail flow rule, use the Except if… option and specify the trusted domains or email addresses.

This way, emails from these friendly domains will not show the External Email Warning or tag, ensuring that legitimate communications are not interrupted.

External Email Warning Examples

Here are a few examples of how an External Email Warning might appear:

Subject Line: “[External Email] Warning: This message comes from outside your organization”
Email Body Warning: “This email has been flagged as coming from an external source. Please exercise caution before clicking on links or opening attachments.”

These warnings help users quickly identify and verify the authenticity of the message.

FAQs

1. Will external email warnings affect internal emails?

No, this rule only applies to emails coming from outside the organization.

2. Can I customize the external email warning message?

Yes, you can modify the message to include any text or alert format that suits your organization.

3. Does this rule work for all versions of Outlook?

Yes, it applies to Office 365, Outlook Web App (OWA), and Outlook desktop versions.

4. Will this slow down email delivery?

No, email tagging in Office 365 is processed instantly and does not impact email speed.

5. How can I test if the rule is working?

Send a test email from an external email account and check if the warning appears in the subject line or message body.

Conclusion

Adding an external email warning in Office 365 and Outlook is a simple yet highly effective way to improve security, prevent phishing attacks, and protect your organization from cyber threats. By following the step-by-step guide in this article, you can successfully enable external email tagging and create a safer email environment.