New Outlook Mandatory Labeling Settings: Location and Practical Limits

Many organizations using Microsoft 365 must apply sensitivity labels to emails and documents. In the new Outlook for Windows, administrators can enforce mandatory labeling so users cannot send unlabeled messages. This article explains where to find these mandatory labeling settings in the Microsoft Purview compliance portal and what practical limits exist when enforcing them. You will learn the exact configuration path, the behavior users see, and the known restrictions that affect label enforcement.

How Mandatory Labeling Works in New Outlook for Windows

Mandatory labeling is a policy setting within Microsoft Purview Information Protection. When enabled for a label policy, new Outlook for Windows requires users to select a sensitivity label before they can send an email. The feature relies on Azure Information Protection (AIP) and the built-in sensitivity labeling engine in Microsoft 365 Apps.

The policy setting is defined at the label policy level, not per individual label. You can create a label policy that includes one or more sensitivity labels and then toggle the mandatory labeling option. The option is named “Require users to apply a label to their email” and appears in the policy configuration wizard under the “Apply a default label to email” section.

When mandatory labeling is active, the new Outlook client blocks the Send action if no label is assigned. The user sees a prompt asking them to choose a label. After selecting a label, the Send button becomes active. The label is applied to the email message and visible in the Sensitivity field in the message header.

Mandatory labeling does not apply to email replies, forwarded messages, or drafts automatically. The enforcement only triggers when the user clicks Send. The label policy also controls whether a default label is applied to new messages, but mandatory labeling is a separate toggle from the default label setting.

Where to Find and Configure the Mandatory Labeling Setting

The configuration is done entirely in the Microsoft Purview compliance portal. You must have the Information Protection Administrator role or equivalent to access these settings.

1. Sign in to Microsoft Purview
   Open a web browser and go to https://compliance.microsoft.com. Sign in with an account that has the Information Protection Administrator role.
2. Navigate to Label Policies
   In the left navigation, expand Information Protection and select Label policies. This page lists all existing sensitivity label policies.
3. Create or edit a label policy
   Click Create a policy to start a new policy. Alternatively, click an existing policy name to edit it. The wizard opens.
4. Choose labels to include
   In the “Choose sensitivity labels to apply” step, select the labels you want to include in this policy. Only labels selected here will be available to users in Outlook.
5. Set the mandatory labeling option
   In the “Apply a default label to email” step, look for the checkbox labeled Require users to apply a label to their email. Check this box. If you also want a default label, select it from the dropdown. The default label is optional. The mandatory labeling checkbox is independent of the default label selection.
6. Assign policy scope
   In the “Assign admin units” step, leave the default to apply to all users or restrict to specific administrative units. In the “Assign users and groups” step, select the users, groups, or distribution lists that will receive this policy. Mandatory labeling only applies to the entities assigned here.
7. Review and finish
   Review the policy settings and click Create or Save. The policy may take up to 24 hours to propagate to all clients. To accelerate, users can restart Outlook or sync the policy manually.

Practical Limits and Known Restrictions

Mandatory labeling only blocks Send for new emails

The mandatory labeling requirement applies only when composing a new email message. Replies, forwards, and meeting requests are not blocked. If a user forwards an unlabeled email, the new message is not subject to mandatory labeling unless the user composes a new message from scratch. This limitation means some unlabeled messages can still leave the organization through reply chains.

No enforcement for shared mailboxes or delegate access

Users who have Send-As or Send on Behalf permissions on a shared mailbox are not required to label messages sent from that mailbox. The mandatory labeling policy only applies to the user’s primary mailbox. If a delegate sends from the shared mailbox, the label policy is not enforced. This gap allows unlabeled messages to be sent from shared mailboxes.

Policy takes up to 24 hours to apply

After you save or update a label policy, the new Outlook client does not enforce the mandatory labeling immediately. The policy is cached locally and refreshed periodically. Users may send unlabeled messages during the propagation window. To force a refresh, users can restart Outlook or run the command Sync-SensitivityLabel in the PowerShell for Microsoft 365 Apps.

Conflicts with multiple label policies

If a user is assigned to more than one label policy, the mandatory labeling setting from the policy with the highest priority takes effect. However, the default label and the list of available labels can be merged. If one policy requires labeling and another does not, the mandatory setting from the higher-priority policy wins. Administrators must verify the priority order in the Label policies list to avoid unintended behavior.

No enforcement for Outlook on the web or mobile

The mandatory labeling setting described here applies only to the new Outlook for Windows desktop client. Outlook on the web and Outlook mobile apps do not enforce this setting. Users on those platforms can send unlabeled messages even when mandatory labeling is enabled. Microsoft plans to extend this feature to other clients but has not provided a timeline.

Labels not visible to external recipients

Sensitivity labels applied to email messages are visible only to recipients inside the same organization. External recipients see no label information in the message header. The label does not affect message encryption or rights management unless the label is configured to apply encryption. Mandatory labeling enforces the presence of a label but does not automatically protect the message content.

Mandatory Labeling vs Default Label vs Automatic Labeling

Item	Mandatory Labeling	Default Label	Automatic Labeling
Description	Blocks Send if no label is applied	Pre-applies a label to new messages	Applies a label based on content detection
User action required	User must pick a label before sending	User can change or remove the default label	User is notified; label applied automatically unless overridden
Scope of enforcement	New Outlook desktop only	All Outlook clients and Office apps	All Outlook clients and Office apps
Propagation delay	Up to 24 hours	Up to 24 hours	Instant after content scan

If Mandatory Labeling Does Not Work as Expected

Send button remains disabled even after selecting a label

This can occur if the label policy has not fully synced to the client. Restart Outlook and wait 15 minutes. If the issue persists, run the Sync-SensitivityLabel PowerShell command on the affected machine. Another cause is a corrupt local label cache. Clear the cache by deleting the folder %LocalAppData%\Microsoft\Office\16.0\SensitivityLabelPolicy and restart Outlook.

Mandatory labeling does not apply to a specific user

Verify that the user is included in the label policy scope. In Purview, open the label policy and check the “Assign users and groups” step. If the user belongs to a group that is not listed, add the group. Also confirm that the policy priority is higher than any conflicting policies that do not require labeling.

Users can bypass mandatory labeling by using classic Outlook

The mandatory labeling setting described in this article applies only to the new Outlook for Windows. Users who switch to classic Outlook for Windows are not subject to this enforcement. To block classic Outlook, administrators can use group policy or Microsoft 365 app settings to remove the classic Outlook option from the user’s device. This is a separate configuration not covered by the mandatory labeling policy.

Conclusion

Mandatory labeling in new Outlook for Windows prevents users from sending unlabeled emails by blocking the Send button until a sensitivity label is selected. The setting is configured in Microsoft Purview under Information Protection > Label policies using the checkbox “Require users to apply a label to their email.” Practical limits include no enforcement for shared mailboxes, no support in Outlook on the web or mobile, and a propagation delay of up to 24 hours. To close the gap for shared mailboxes, consider using a transport rule that rejects unlabeled messages. For mobile users, educate them to apply labels manually until Microsoft extends mandatory enforcement to those clients.