How To: Exchange Online External E-mail Tagging

Recently I wrote a blog post about using the First Contact Safety Tip, in which I mentioned that many organizations nowadays add a brief warning message in the e-mail content body warning recipients that the e-mail originates from an external sender. As a side effect, this also means the message is usually included in any replies. A few months ago, Microsoft introduced a new way to flag such e-mails, without modifying the content of the actual e-mail.

As you can see from the above screenshot, after enabling this functionality, e-mails received from an external sender will now show an ‘External’ tag and a mail tip stating that the sender is outside your organization. No additional text is added into the e-mail body.

Enabling / Disabling External E-mail Tagging

You can enable or disable this feature by using Exchange Online PowerShell, specifically the Set-ExternalInOutlook and Get-ExternalInOutlook cmdlets:

  • Enable the functionality: Set-ExternalInOutlook -Enabled:$True
  • Disable the functionality: Set-ExternalInOutlook -Enabled:$False
  • Check the current settings: Get-ExternalInOutlook

You can also add domains or e-mail addresses into an ‘allow list’, which will prevent e-mails from these specific senders from being marked as external. For this, you can use the Set-ExternalInOutlook cmdlet with the AllowList parameter:

Set-ExternalInOutlook -AllowList @{Add="[email protected]"; Remove="[email protected]"}

It may take 24-48 hours before the change is active. Keep in mind that external e-mail tagging requires your users to use an up-to-date Outlook client (web, Windows, macOS/iOS/iPadOS, Android), as it relies on specific Outlook functionality. If your organization uses other third-party e-mail clients, and you would like to use an external sender warning, please use the ‘mail flow rule’ option instead to modify the e-mail content.