How to prepend Office 365 email subject when email is received from External sender.

Last updated on Apr 1, 2020

How to prepend Office 365 email subject when email is received from External sender.

In this post I will look at how you can quickly append a warming when an email is sent from an external sender to safeguard your users from unknown senders.

To get started, login to the Office 365 Admin Portal. https://portal.office.com

Then under Admin centers click on Exchange

From the Exchange Admin center, click on Mail Flow

Then on the right-hand side click on + then select create new rule.

Then on the new rule page, provide a name for the new rule “Warning Message” and select the Sender is located outside the organisation.

Then add an additional condition and select Recipient is located inside the organisation.

Under Do the following click select Apply disclaimer and select Prepend a Disclaimer

Click on Enter text and provide a html code for the warning message the below can be used.

<p><div style=’border:solid #9C6500 1.0pt;padding:2.0pt 2.0pt 2.0pt 2.0pt’><p class=MsoNormal style=’line-height:12.0pt;background:#FFEB9C’><b><span style=’font-size:10.0pt;color:#9C6500′></span></b><span style=’font-size:10.0pt;color:black’> [EXTERNAL]<o:p></o:p></span></p>

Click on ok

Then click on *select one … and select wrap

Click on Add condition and click on Prepend the subject of the message with…

Click on *Enter text and Type: [EXTERNAL]

Click on *Enter text and Type: [EXTERNAL] then click ok.

Once done click on save.

By adding the Prepend disclaimer you will have a Stamp on the email body saying [External] and your email subject will be stamped with [EXTERNAL] as well.

You can now test the newly created Transport rule by sending an email from any external domains to your Office 365 account and notice the addition in the mail subject line.

Example below.

If it’s too much to have both the Subject and the Body of the email stamped, you can then remove the Prepend disclaimer option and only have the Prepend subject of a message.

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