Partly. Microsoft documents a setting that switches signatures off for Outlook on the web, the new Outlook for Windows and Outlook for Mac; it names a policy for classic Outlook for Windows without documenting its menu path; and for Outlook on iOS and Android it documents no setting that locks the signature. This guide goes client by client, and every cell of the table points to the Microsoft page it comes from.
SignaturesEnabled), Outlook for Mac has its own preference (DisableSignatures), classic Outlook has an ADMX policy called disablesignatures, and the mobile apps have nothing that locks the signature. Note also that these settings switch signatures off: they do not impose the company signature.
Why is blocking signatures not the same as imposing one?
The Microsoft settings below do one thing: they stop users from creating, editing or using a signature in a given client. Read the wording of the Learn pages: for Outlook on the web, $false means "Signatures aren't available in Outlook on the web"; for Outlook for Mac, the preference prevents users from creating, editing and adding client-side signatures. None of them places a company signature in the message.
To get both, a locked client and a consistent signature, an administrator needs a second mechanism that inserts the signature. Microsoft Learn does not say how an inserted signature interacts with each of these settings, so try the combination on a pilot mailbox before you roll it out.
How do you lock the Outlook signature, client by client?
| Client | Method documented by Microsoft | Source |
|---|---|---|
| Outlook classic for Windows | ADMX policy named disablesignatures (internal name L_DisableSignatures): "Specifies whether users can add signatures to e-mail messages." Menu path, label shown in the editor and Intune procedure: not documented by Microsoft. | Map classic Outlook policies to new Outlook |
| New Outlook for Windows | The Outlook on the web mailbox policy: Set-OwaMailboxPolicy -SignaturesEnabled $false, or the Exchange admin center. The ADMX policies of classic Outlook do not apply. | Policy management in new Outlook for Windows |
| Outlook on the web (OWA) | Set-OwaMailboxPolicy -SignaturesEnabled $false; default value $true. | Set-OwaMailboxPolicy |
| Outlook for Mac | Preference DisableSignatures in the com.microsoft.Outlook domain (Boolean, true to disable), available from version 16.18, configuration profile required. | Set preferences for Outlook for Mac |
| Outlook for iOS | No setting that locks the signature is documented. Intune only sets the app's default signature, and users can add their own even when it is disabled. | Outlook for iOS and Android configuration with Intune |
| Outlook for Android | Same as iOS: no setting that locks the signature is documented; only the app's default signature can be switched on or off. | Outlook for iOS and Android configuration with Intune |
For classic Outlook, Learn only states where Outlook ADMX policies appear: "User Configuration (Enabled) > Policies > Administrative Templates > Microsoft Outlook 2016/<policy category>". It does not give the category or the label of this particular policy. For the file-and-registry route that predates it, see the Outlook signature via GPO.
How do you switch signatures off in Outlook on the web and the new Outlook?
In Exchange Online PowerShell, on the default policy (Learn says the default Outlook on the web mailbox policy is named OwaMailboxPolicy-Default in Exchange Online):
Set-OwaMailboxPolicy -Identity OwaMailboxPolicy-Default -SignaturesEnabled $falseOr in the Exchange admin center, as described on Microsoft's policy management page:
- Open the Outlook web app policies page.
- Select the name of the policy, then Manage features in the Features section.
- Expand User experience and uncheck Email signature.
- Select Save changes.
Learn notes that changes to Outlook on the web mailbox policies might take up to 60 minutes to take effect. The same Learn page that describes this setting for the new Outlook for Windows words it for "Outlook on the web users"; the mapping table of classic policies is what ties SignaturesEnabled to disablesignatures in the new Outlook.
What can an add-in do, and what does ATOM Signatures do?
Microsoft gives add-ins their own method, disableClientSignatureAsync, which disables the Outlook client signature. Per Microsoft Learn, its behavior depends on the client:
- Outlook on the web and new Outlook for Windows: the signature option for new mails, replies and forwards is disabled, and a selected signature is also disabled.
- Outlook classic for Windows and Mac: the signature under "New messages" and "Replies/forwards" of the sending account is set to (none).
- Outlook on Android and iOS: the signature saved on the mobile device is cleared.
On mobile, Learn lists this method as available from Outlook version 4.2352.0 (Mailbox 1.10). It is a mechanism of add-ins in general.
ATOM Signatures does not call it. It does not lock or clear the native signature. What the administrator controls is the content: the signature templates are managed in the console. In the task pane, users choose among the signatures assigned to them, and they can edit their contact details only if the administrator turns that option on; it is off by default. To compare this with relying on native settings alone, see ATOM vs the native Microsoft 365 signature.
Related reading: signatures in the new Outlook, Outlook signatures on Mac and mobile and why Set-MailboxMessageConfiguration no longer sets signatures.
Frequently asked questions
Can you lock Outlook signatures in Microsoft 365?
Partly. Microsoft documents a setting that switches signatures off for Outlook on the web and the new Outlook for Windows (SignaturesEnabled on Set-OwaMailboxPolicy) and for Outlook for Mac (the DisableSignatures preference). For classic Outlook for Windows it lists a policy named disablesignatures without its menu path, and for Outlook on iOS and Android it documents no setting that locks the signature.
How do I disable signatures in Outlook on the web?
With Set-OwaMailboxPolicy -Identity OwaMailboxPolicy-Default -SignaturesEnabled $false in Exchange Online PowerShell, or in the Exchange admin center by unchecking Email signature under User experience in the policy's features. Microsoft says changes to these policies can take up to 60 minutes to take effect.
Does ATOM Signatures lock the native Outlook signature?
No. ATOM does not call disableClientSignatureAsync, so it neither locks nor clears the signature built into Outlook. The administrator manages the content of the templates in the console, users choose among the signatures assigned to them, and they can edit their contact details only if the administrator turns that option on (off by default).
Can users still add their own signature in Outlook mobile?
Microsoft documents no setting that prevents it. On its Intune page for Outlook for iOS and Android, Microsoft states that users can add their own signatures even when the app's default signature is disabled.
Manage the signature content in one place. ATOM Signatures costs CA$1 per user per month, plus taxes, with a 14-day free trial.
Sources
- Microsoft Learn — Set-OwaMailboxPolicy (SignaturesEnabled, default policy name, 60 minutes): learn.microsoft.com
- Microsoft Learn — Policy management in new Outlook for Windows (Disable signatures): learn.microsoft.com
- Microsoft Learn — Map classic Outlook policies to new Outlook (disablesignatures): learn.microsoft.com
- Microsoft Learn — Set preferences for Outlook for Mac (DisableSignatures): learn.microsoft.com
- Microsoft Learn — Outlook for iOS and Android configuration with Microsoft Intune (default app signature): learn.microsoft.com
- Microsoft Learn — Office.MessageCompose, disableClientSignatureAsync: learn.microsoft.com
- Microsoft Learn — Outlook JavaScript APIs supported in Outlook on mobile devices: learn.microsoft.com
Sources consulted on November 2, 2026.