Email Signatures in the New Outlook, Outlook on the Web and Outlook Mobile: An IT Guide (2026)

TL;DR: The new Outlook for Windows runs on the same web architecture as Outlook on the web, stores signatures in the mailbox (roaming signatures) and does not run COM or VSTO add-ins. That makes web add-ins using the OnNewMessageCompose event the one client-side mechanism that covers the new Outlook, Outlook on the web, classic Outlook, the new Outlook for Mac and Outlook for iOS and Android. Microsoft has moved the enterprise opt-out phase, when the new Outlook becomes the default, to March 2027. Before then, IT should retire file- and script-based signatures, confirm an admin-deployed add-in works in every client, and decide how to cover Apple Mail and other non-Outlook apps.

Last reviewed: October 2026.

Most companies still run a mix of Outlook clients: classic Outlook on managed Windows laptops, the new Outlook on a growing number of machines, Outlook on the web on shared and personal computers, and the Outlook apps on phones. Each one used to store and insert signatures differently, which is why signatures drift. This guide explains what the new Outlook changes, which signature methods work in which client, how to manage Outlook on the web and Outlook mobile specifically, and what to check before Microsoft makes the new Outlook the default. Tenant-wide deployment steps are in the Microsoft 365 rollout guide. If you only need to change your own signature, see Scribe's posts on changing your signature in Outlook 365 and adding a signature in Outlook on iPhone.

What changed with the new Outlook for Windows?

Three changes matter for signatures.

• It is built on the web client. Microsoft describes the new Outlook as "inspired by the Outlook web experience" and running on WebView2, with features delivered from the service rather than through Office update channels (Microsoft Learn: overview of the new Outlook for Windows). In practice, a signature that works in Outlook on the web will behave the same way in the new Outlook.
• COM add-ins are gone. "In new Outlook for Windows, COM add-ins aren't supported." Existing web add-ins "are fully supported, with no extra work required" (same source). Any signature tool that relies on a COM or VSTO add-in, or on a desktop agent writing files into the classic Outlook signature folder, stops working when a user switches.
• Signatures live in the mailbox. With roaming signatures, Outlook stores signatures in the user's mailbox so they follow the account across devices. Microsoft documents this for Outlook for Windows build 2303 and later, for mailboxes on Microsoft 365 or Outlook.com; Exchange on-premises, third-party and POP/IMAP accounts don't roam (Microsoft Support: Outlook roaming signatures).

The timeline IT should plan against

Microsoft's rollout has three phases: opt-in (users can toggle to the new Outlook), opt-out (the new Outlook becomes the default but users can switch back) and cutover (no way back). In Message Center post MC949965, last updated February 2026, Microsoft says "the opt-out phase for Enterprise environments will now begin in March 2027 (previously April 2026)", with dates for GCC High and DoD to follow. Existing policies that block or hide the new Outlook keep applying, and admins can stage migration by Entra ID group (MC949965 mirror). Microsoft has not published a cutover date. Meanwhile its own Learn overview still describes the new Outlook as "a preview for commercial accounts", so expect the wording and dates to move again and check the Message Center rather than relying on this paragraph.

Which Outlook versions can get a centrally managed signature?

There are three ways to put a company signature on Outlook mail: write it into each client's settings, insert it with an admin-deployed add-in when the user starts writing, or add it in transit on the server. The add-in route depends on Outlook's event-based activation: when a user starts a new message, reply or forward, Outlook raises OnNewMessageCompose and the add-in calls setSignatureAsync. Microsoft lists that event for Outlook on the web, the new and classic Outlook for Windows, the new Outlook for Mac, Android and iOS (Microsoft Learn: activate add-ins with events).

Client	Native admin control	Event-based add-in	Server-side (in transit)
Outlook on the web	Set-MailboxMessageConfiguration, only if roaming signatures are disabled	Yes	Yes
New Outlook for Windows	Same as Outlook on the web	Yes	Yes
Classic Outlook for Windows	None centrally; registry can disable roaming	Yes, on supported builds (Windows 10 1903 or later)	Yes
New Outlook for Mac	None centrally	Yes (add-in only manifest)	Yes
Legacy Outlook for Mac	None centrally	No	Yes
Outlook for iOS and Android	Intune can turn off the "Get Outlook" default signature	Yes, Outlook 4.2352.0 and later (add-in only manifest)	Yes
Exchange on-premises mailboxes	Transport rules on the server	Depends on the vendor	Depends on mail flow

Two constraints are easy to miss. First, event-based add-ins only launch automatically when an administrator deploys them, not when users install them themselves, unless the vendor has an unrestricted Marketplace listing. Second, add-ins built on the unified manifest for Microsoft 365 aren't supported on Mac or mobile, so vendors need an add-in only (XML) manifest to cover those clients (both from the event-based activation page above).

Server-side routing covers every client because the signature is added after the message leaves the mailbox. The trade-off is that users don't see the signature while writing and the Sent Items copy doesn't include it. The client-side vs server-side guide compares the two in detail.

How do you manage signatures in Outlook on the web?

What users see

In Outlook on the web, users open Settings, then Account, then Signatures, and pick default signatures for new messages and for replies and forwards. In the new Outlook the path is Settings > Accounts > Signatures (Microsoft Support: add and change a signature in Outlook). Whatever a user saves here roams to their other roaming-aware clients, which is the opposite of what IT wants from a managed signature.

What admins can set natively

Exchange Online's Set-MailboxMessageConfiguration cmdlet has SignatureHtml, AutoAddSignature and AutoAddSignatureOnReply parameters, but they only work when roaming signatures are off. Microsoft added an organization-level switch for that: setting PostponeRoamingSignaturesUntilLater to $true with Set-OrganizationConfig disables roaming signatures in Outlook on the web and the new Outlook, after which "admins can use the signature-related parameters on the Set-MailboxMessageConfiguration cmdlet" (Microsoft Learn: Set-OrganizationConfig). Classic Outlook needs the separate DisableRoamingSignatures registry value, set per user or through Group Policy under HKEY_CURRENT_USER\SOFTWARE\Policies\Microsoft\Office\16.0\Outlook\Setup (roaming signatures article above).

That gets one HTML block per mailbox, pushed by script. It doesn't fill in directory data on its own, doesn't vary by reply or internal recipient, and has to be re-run whenever a title or phone number changes. It's a reasonable stopgap for a small tenant; it isn't a signature program.

What an add-in changes

An admin-deployed signature add-in doesn't depend on the roaming setting, because it inserts the signature into the message being composed rather than editing the stored one. It also re-applies the approved version each time a user starts writing, so a manual edit in settings doesn't survive. Scribe documents exactly that behavior: the approved signature is injected "every time a teammate opens the compose window in Gmail or Outlook", regardless of what's saved in the client (Scribe: manual edits).

Troubleshooting Outlook on the web

• Add-in deployed but nothing appears. Microsoft says admin-deployed add-ins can take up to 72 hours to show up, and Scribe allows up to 72 hours for Microsoft validation (Scribe: Microsoft 365 add-in). Check that the add-in appears under Integrated apps in the Microsoft 365 admin center and was assigned to the right users.
• Installation stuck for one user. For Scribe, the documented fix is to sign out of Scribe and back in, then contact support (Scribe: Outlook Web add-in signatures not being installed).
• Signature missing on some surfaces. Microsoft notes that in Outlook on the web and the new Outlook, event-based activation "may not work when composing on some non-standard surfaces", such as replying to a meeting invite with RSVP with note or forwarding a meeting from the calendar (event-based activation page above). That's a platform limit, not a misconfiguration.

How do signatures work in Outlook for iOS and Android?

Outlook mobile keeps its own signature setting in the app, and when no custom signature is defined it adds its default "Get Outlook for iOS" or "Get Outlook for Android" line. Admins can turn that default off with an Intune app configuration policy (setting Default app signature, key com.microsoft.outlook.Mail.DefaultSignatureEnabled set to false); users can still add their own signature (Microsoft Learn: Outlook for iOS and Android configuration with Intune). CodeTwo has reported that this policy blocked all signatures in Outlook for Android at one point, which Microsoft treated as a bug (CodeTwo KB). We haven't verified the current state, so test it on an Android device before you apply it widely.

Add-ins on mobile

Outlook mobile officially supports the Office.js API up to Mailbox requirement set 1.5, but Microsoft has enabled the pieces a signature add-in needs, including setSignatureAsync and disableClientSignatureAsync, and supports OnNewMessageCompose from Outlook version 4.2352.0 on both iOS and Android (Microsoft Learn: event-based activation in Outlook mobile add-ins). The same page lists behaviors to expect in testing:

• If the user has a signature saved on the device, "it will briefly appear in the message you create, but will be immediately replaced by the signature added by the add-in."
• An add-in may run for at most 60 seconds, and only one add-in runs at a time.
• The event doesn't fire when a message is created from the Share option on iOS.
• When replying from the bottom of a message, the signature is added but isn't visible until the compose window is expanded to full screen.

For Scribe specifically, the Microsoft 365 add-in lists Web, Desktop, iOS and Android as supported platforms. Some add-in updates can't be applied automatically and must be approved once by an admin in Integrated apps, and Scribe names "automatic signature installation for iOS and Android Outlook apps" as one of the reasons to approve them (Scribe: update the Microsoft add-in). If mobile signatures are missing in a tenant where desktop works, check for a pending update first.

When the add-in isn't enough

Users who read company mail in Apple Mail, Gmail or another app on their phone are outside Outlook's reach. Server-side routing is the only way to cover them; see the mobile signatures guide for the app-by-app picture.

What about classic Outlook and devices without a Microsoft 365 license?

Classic Outlook isn't going away overnight. Microsoft's own add-in documentation still covers it, and event-based add-ins run there on Windows 10 version 1903 or later. Scribe lists minimum classic Outlook builds for its add-in: version 16.0.14026.20000 on Current Channel, 16.0.14131.20000 on Monthly Channel and 16.0.14326.10000 on Semi-Annual Channel. On the Mac, the add-in works only in the new Outlook for Mac, version 16.54 (21101001) or later (Scribe: Outlook add-in not validating). Scribe's own first-line fix when a signature doesn't insert or display correctly is to switch the user to the new Outlook (Scribe: switch to new Outlook).

Machines whose users don't have a Microsoft 365 cloud license, such as Outlook against an on-premises or third-party mailbox, can't use a tenant-deployed add-in. For those, Scribe offers a desktop app. On Windows it can be pushed silently with any RMM tool: deploy a DomainToken registry value under HKLM:\SOFTWARE\Policies\Scribe\Config, then run the installer with /S; an optional DisableAutoUpdate value turns off auto-update (Scribe: Outlook Windows RMM). On the Mac, the app ships as a DMG for RMM deployment (Scribe: Outlook Mac RMM). Scribe states these integrations are "only required for users who don't have a Microsoft 365 cloud license."

How do you troubleshoot signatures across Outlook clients?

Symptom	Likely cause	Fix
Old signature reappears after a script set the new one	Roaming signatures overwrote the scripted value	Set PostponeRoamingSignaturesUntilLater or move to an add-in
Signature tool stopped working after a user toggled to the new Outlook	COM/VSTO add-in or file-based agent	Replace with a web add-in or server-side routing
Add-in signature missing for everyone after deployment	Propagation (up to 72 hours) or add-in not assigned to the users	Check Integrated apps assignment; wait out the window
Works on desktop, missing on Outlook mobile	Outdated add-in version, unified-manifest-only add-in, old app version	Approve the pending update; confirm Outlook 4.2352.0 or later
"Get Outlook for iOS" still appended	App default signature	Intune DefaultSignatureEnabled = false, tested on Android first
Missing on calendar replies or meeting forwards	Non-standard compose surface	Expected platform limit; cover with server-side if required
Classic Outlook on an old build ignores the add-in	Below the minimum build or Windows 10 1903	Update the channel, or switch the user to the new Outlook
Signature looks different in classic Outlook	Classic Outlook renders HTML with Word, which ignores some CSS	See the image and rendering guide

What should IT check before the new Outlook becomes the default?

1. Inventory how signatures get there today. Logon scripts writing to %APPDATA%\Microsoft\Signatures, COM add-ins, desktop agents and transport rules each fail differently in the new Outlook. Microsoft has a guide to identifying COM add-ins in your tenant (Microsoft Learn: migrate COM add-ins to web add-ins).
2. Decide on roaming. Either leave roaming on and use an add-in or server-side, or turn it off with PostponeRoamingSignaturesUntilLater and the classic Outlook registry value if you script signatures. Don't run both a script and roaming.
3. Deploy the add-in to a pilot group first and give it the full 72 hours before judging it.
4. Test every client with the same account: Outlook on the web, the new Outlook, classic Outlook, Outlook for Mac, Outlook for iOS and Android. Test new message, reply, forward, a shared mailbox and a send-as alias.
5. Check mobile specifically: app version, add-in update status, and the Intune default-signature setting.
6. List who sits outside Outlook: Apple Mail users, Gmail app users with company accounts, CRM and sequencer tools sending through the mailbox. Decide whether server-side covers them.
7. Use the migration policy controls. MC949965 describes admin-controlled, Entra ID group-scoped migration, so you can move departments only after their signature checks pass.
8. Write the help-desk script for "my signature disappeared after I switched Outlook", which will be the most common ticket during the opt-out phase.

Where does Scribe fit across Outlook clients?

Scribe's Microsoft 365 add-in is deployed once by a Global Admin from the Microsoft Marketplace to the entire organization and covers Outlook on the web, desktop (classic and new on Windows, new Outlook for Mac), iOS and Android. It shows each teammate's signature status (Pending until they next compose an email, then Installed) so you can see rollout progress per person (Scribe: installation statuses). It supports on-reply and internal variants in Outlook on paid plans (Scribe: signature variants). For Apple Mail, other mobile apps and tools sending through the mailbox, add Microsoft 365 server-side routing; when both are connected, Scribe uses the add-in where it can and server-side as the fallback (Scribe: mobile). Unlicensed Windows and Mac machines get the RMM-deployable desktop app. Directory data comes from Microsoft Entra ID; Scribe doesn't document an on-premises Active Directory connector. You can also check install status across the tenant from an AI assistant through Scribe's MCP server.

Frequently asked questions

Can an admin set one signature for every user in Outlook on the web?

Natively, only by script and only with roaming signatures turned off: set PostponeRoamingSignaturesUntilLater to $true with Set-OrganizationConfig, then push HTML with the SignatureHtml and AutoAddSignature parameters of Set-MailboxMessageConfiguration. An admin-deployed signature add-in works without changing the roaming setting and fills in each user's own details.

Does the new Outlook for Windows support signature add-ins?

It supports web add-ins, including the OnNewMessageCompose event that signature add-ins use, but not COM or VSTO add-ins. Tools that wrote signature files for classic Outlook or ran as COM add-ins stop working when a user switches.

When will the new Outlook become the default for companies?

Microsoft's Message Center post MC949965, updated in February 2026, says the opt-out phase for Enterprise environments begins in March 2027, moved from April 2026. Users can still switch back during that phase, and existing policies that block or hide the new Outlook keep applying. No cutover date has been announced.

Why do Outlook mobile emails end with "Get Outlook for iOS"?

Outlook for iOS and Android adds that default line when no custom signature is defined. Admins can turn it off with the Intune app configuration setting Default app signature, key com.microsoft.outlook.Mail.DefaultSignatureEnabled set to false. Test on Android first, because a past bug made the setting block all signatures there.

Do signature add-ins work in Outlook for iPhone and Android?

Yes, if the vendor ships an add-in only manifest and the admin deploys it. Microsoft supports OnNewMessageCompose in Outlook for iOS and Android version 4.2352.0 and later. Scribe's Microsoft 365 add-in lists iOS and Android as supported, and some updates must be approved in Integrated apps to enable mobile installation.

Do roaming signatures break centrally managed signatures?

They break scripted and file-based signatures, because Outlook overwrites them with the version stored in the mailbox. Add-ins and server-side routing don't depend on the roaming setting, since they insert the signature into the message rather than editing the stored one.

Does Scribe work in Outlook for Mac?

Scribe's add-in works in the new Outlook for Mac, version 16.54 (21101001) or later. Users without a Microsoft 365 cloud license can use the Scribe desktop app, which IT can deploy as a DMG through an RMM tool.

How long until a deployed signature add-in shows up?

Microsoft says admin-deployed add-ins can take up to 72 hours to appear, and Scribe allows up to 72 hours for Microsoft validation. In Scribe, each teammate's signature shows Pending until they next compose an email, then Installed.

Related Handbook guides

• Microsoft 365 company-wide signature rollout
• Client-side vs server-side email signatures
• Company email signatures on mobile
• Sync signatures with Microsoft Entra ID
• Shared mailbox, alias and reply signatures
• Email signature rollout playbook