Why doesn't Set-MailboxMessageConfiguration set signatures anymore?

What changed to make the script stop working?

Microsoft calls it roaming signatures: signatures are stored in the mailbox, in the cloud, so they follow an account to every device. Microsoft's page Outlook roaming signatures says the feature works with Microsoft 365 and Outlook.com mailboxes and that it is available for Outlook build 2303 or higher. It adds that add-ins which write signatures to the local drive or the registry no longer work when the feature is on.

Microsoft's reference for the cmdlet, Set-MailboxMessageConfiguration, is explicit about the consequence for AutoAddSignature: "This parameter doesn't work if the Outlook roaming signatures feature is enabled in your cloud-based organization." The same page says that when roaming signatures are disabled, administrators can use the signature-related parameters again, for example AutoAddSignature, AutoAddSignatureOnReply and SignatureHtml.

On the date: Symprex's support article OWA signatures are not updating in Microsoft 365 states that "Microsoft enabled the roaming signatures feature on all Microsoft 365 tenants in April 2023". That is Symprex's statement, not Microsoft's.

What do the signature parameters of Set-MailboxMessageConfiguration do?

Here is the syntax from Microsoft Learn, cut down to the signature parameters:

Set-MailboxMessageConfiguration [-Identity] <MailboxIdParameter>
 [-AutoAddSignature <Boolean>]
 [-AutoAddSignatureOnMobile <Boolean>]
 [-AutoAddSignatureOnReply <Boolean>]
 [-SignatureHtml <String>]
 [-SignatureName <String>]
 [-SignatureText <String>]
 [-SignatureTextOnMobile <String>]

A call has the same form as the examples on that page, an identity followed by parameters:

Set-MailboxMessageConfiguration kai@contoso.com -AutoAddSignature $true -SignatureHtml "<p>Kai Klein, Contoso</p>"

Note what the descriptions say: these parameters are written for Outlook on the web. Even when they work, they are not a way to place a signature in classic Outlook for Windows or in the Outlook mobile apps.

How do I turn roaming signatures off?

Microsoft added a switch to Set-OrganizationConfig. Learn notes that, previously, the only way to disable roaming signatures in Outlook on the web was to open a support ticket. In Exchange Online PowerShell:

Set-OrganizationConfig -PostponeRoamingSignaturesUntilLater $true

Per Learn, $true means roaming signatures are disabled and $false means they are enabled, which is the default. Once they are disabled, the call to Set-MailboxMessageConfiguration above is usable again.

For classic Outlook on Windows, Learn says the registry setting to disable roaming signatures still works. Microsoft's roaming signatures page documents it as a DWORD value:

Key:   HKCU\Software\Microsoft\Office\16.0\Outlook\Setup
Name:  DisableRoamingSignatures
Type:  DWORD
Value: 1

The same page also lists the policy location, HKCU\SOFTWARE\Policies\Microsoft\Office\16.0\Outlook\Setup, for settings pushed by Group Policy. For that route, see signatures and Group Policy.

What are the limits of PostponeRoamingSignaturesUntilLater?

• Which clients. Learn says the parameter controls roaming signatures in Outlook on the web and in the new Outlook for Windows. It does not cover classic Outlook for Windows, which has its own registry setting.
• Cloud only. Learn says the parameter is available only in the cloud-based service.
• It is an opt-out. The default is $false: roaming signatures are on until your organization turns them off.
• It is a postponement. The name says so, and Microsoft Learn gives neither a duration nor an end date for it (checked November 2, 2026). Symprex writes that, even if you later disable roaming signatures, Microsoft is known to re-enable them at a later date. Plan as if the switch may stop working.
• It is not Microsoft's recommended path for signature tools. Learn states: "We recommend that independent software vendors (ISVs) onboard to the signature API based on event-based hooks. We have no plans to support roaming signature management in the Microsoft Graph API."
• It does not make the cmdlet a deployment tool. Its syntax takes one mailbox identity at a time and its parameters are written for Outlook on the web; nothing in it targets groups or departments.

What should I do for the long term?

Treat the postponement as time to move, not as a fix. Microsoft's own direction is an add-in built on event-based hooks, which inserts the signature as the message is composed instead of writing it into the mailbox. Three practical steps:

1. Decide whether you still need the script: list who gets which signature and why.
2. Choose a tool that does not depend on the cmdlet; the guide Leaving Email Signature Manager before EWS shuts down gives neutral criteria, and the EWS retirement guide covers the other dated change that affects signature tools.
3. If you use the new Outlook, read the new Outlook signature guide, which explains where signatures are stored there.

ATOM Signatures works the other way around. It uses no PowerShell against your mailboxes: it reads the directory through Microsoft Graph, in application mode and read-only, and the add-in inserts the signature with setSignatureAsync as the message is composed. ATOM does not lock the native signature (it does not call disableClientSignatureAsync). For how this compares with doing it natively, see ATOM vs the native Microsoft 365 signature.

Frequently asked questions

Sources

• Microsoft Learn — Set-MailboxMessageConfiguration (syntax, signature parameters, roaming signatures): learn.microsoft.com
• Microsoft Learn — Set-OrganizationConfig, PostponeRoamingSignaturesUntilLater: learn.microsoft.com
• Microsoft Support — Outlook roaming signatures (build 2303, DisableRoamingSignatures): support.microsoft.com
• Symprex — OWA signatures are not updating in Microsoft 365 (April 2023, re-enabling): support.symprex.com

Sources consulted on November 2, 2026.