Implement external banner using exchange online

Some of the company do not enable external banner for sender outside of the organization.

In this blog, we will perform a basic and yet, effective banner so all users are being informed or reminded for their safety every time they receive an email from external.

We have 2 goals:

1. Create a company's custom banner for external emails

2. Insert EXTERNAL tag in the email subject without duplication

Lets get started:

Create Mail flow rule for External banner message

1. Login to exchange admin center

2. Click Mail flow > Rules

3. Click Add a rule > Create a new rule

4. Fill this up:

Name: External message warning rule

Apply this rule if: The sender: is External/Internal > Outside the Organization

CLICK Add a new condition

The recipient: is External/Internal > Inside the Organization

Do the following: Apply a disclaimer to the message : prepend a disclaimer

CLICK enter text:

Prepend  '<p style="border:1px; border-style:solid; border-color: #FFCACA; background-color: #FFCACA; padding: 1em;"> <span style=font-size:12.0pt;color:black;><b>[EXTERNAL EMAIL]</span></b> <span style=font-size:10.0pt;color:black> CAUTION: This email originated from outside Company's systems. Do not click links or open attachments unless you recognize the sender and know the content is safe.</span></p> '

fallback to action : Wrap

5. Click Save > Confirm

6. If neccessary, Enable this rule (normally it is disabled even after enabling it upon rule creation)

Create Mail flow rule for External tag

1. login to exchange admin center

2. Click Mail flow > Rules

3. Click Add a rule > Create a new rule

4. Fill this up:

Name: External message warning rule

Apply this rule if: The sender: is External/Internal > Outside the Organization

CLICK Add a new condition

The recipient: is External/Internal > Inside the Organization

do the following: prepend the subject of the message with : specified prefix = [EXTERNAL]: 

Except if: The subject or body : subject matches these text patterns : [EXTERNAL]: 

(The purpose of this is to prevent adding subject tag repeatedly for each email messages from external. if this exception is not configure, the result email subject for long email conversation will be:)

5. Click Save > Confirm

6. If necessary, Enable this rule (normally it is disabled even after enabling it upon rule creation)

TEST:

1. Send email from Gmail account into corporate account with the Email subject: "Final test" and here is the result:

This is a simple way to implement External banner.

Hope it helps.

Thank you :)