External email warning rule – Exchange Online

Many companies choose to include in the first line of an email a message indicating that the email comes from an external source.

Such a notification might look like this:

Adding such a banner at the top of an email serves as a reminder to employees to verify the sender, message content, and attachments. You can customize the text to suit your company’s specific needs.

To include this banner in emails, you can create a rule in Exchange Online that inserts a specific HTML code into each email.

Let’s start by preparing the HTML banner. We’ll use an online HTML editor for this purpose.

Here’s an example of what the HTML code might look like:

Now that we know what we want to add to the message, let’s move on to the next step to Exchange Online admin panel.

In the next step will add new rule. For the test purposes I configured it like below.

Now we need to save the changes, and finally, enable the rule. After a few minutes, the information added in the rule will appear in emails received from outside the organization.