External Tags Suddenly Forced

Question

Suddenly the other day everyone got the External tag applied to outside emails. I went in and confirmed it was not on via PowerShell, disabled it, but the next day it was enabled again. Every time it is turned off it shows enabled again by the next day. We did not make any policy changes or other adjustments to our tenant prior to this suddenly starting. I have tried to locate some sort of policy in Defender or Exchange that may be enforcing it but have not had any luck.

Answer 1

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Hi @tstone wc

Can you please confirm if you are seeing the External tag like this?

For the temporary solution, if you are using Classic Outlook, you can follow the steps here to hide it. Remove “External” tag from Outlook Message List - Robert 365

I know this is not a definite solution, but meanwhile figuring this out, please use it as an alternative.

You mentioned you already checked via PowerShell; did you use this one? And the value shows false, right?

Get-ExternalInOutlook

Can you also double check if you have any transport rule configure in Exchange Admin Center?

I look forward for your reply.

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Answer 2

External sender tagging in Outlook is controlled by the external sender identification feature in Exchange Online, not by a client-side setting. If it keeps re-enabling, the configuration is being set at the service level and will override manual changes.

Key points and actions:

1. Verify the tenant-wide external sender configuration
   • Use the Exchange Online PowerShell cmdlet that manages this feature:
     • Set-ExternalInOutlook is used to modify external sender identification for Outlook, Outlook for Mac, Outlook on the web, and Outlook for iOS and Android.
   • Check the current configuration (for example, via Get-ExternalInOutlook) and confirm whether Enabled is set to $true at the organization level.
   • If the organization previously used mail flow rules to prepend subjects for external mail, those rules should be disabled when this feature is enabled to avoid duplication, as the service-level feature is the supported mechanism.
2. Stop fighting the service-level setting per day
   • If Enabled is being reset to $true daily, it is likely being enforced by:
     • An automated configuration process (e.g., a script or configuration-as-code pipeline) that runs on a schedule, or
     • An admin or security baseline that standardizes external sender identification.
   • Instead of toggling it off ad hoc, identify and update the source of truth (script, policy, or baseline) that is applying Set-ExternalInOutlook -Enabled $true.
3. Check for other external-tag mechanisms
   • If the organization previously used transport rules to prepend text to subjects for external senders, those rules should be disabled when using the external sender identification feature, as recommended in the cmdlet description. Leaving both in place can cause confusion and make it appear as if the feature is “coming back” when in fact multiple mechanisms are active.
4. Confirm client behavior
   • Once the organization-level configuration is set as desired (for example, Set-ExternalInOutlook -Enabled $false and no automation is re-enabling it), Outlook on all platforms (desktop, web, mobile) will follow that configuration for external sender identification.

In summary, external tags are controlled centrally via Set-ExternalInOutlook. To stop them from reappearing, locate and modify or remove any automated or baseline configuration that is repeatedly setting Enabled to $true, and ensure any legacy mail flow rules for external tagging are disabled if relying on this feature.

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References:

• Set-ExternalInOutlook
• What is the External label on Outlook mobile email?
• Why is there no External label or External mail tooltip on an External email?