1. Who this guide is for
ATOM Signature is an Outlook add-in that automatically applies the email signature your organization has defined, when a message is composed and sent. Deployment happens once, for the whole organization, done by an administrator — end users have nothing to install.
This guide is for Microsoft 365 administrators deploying the add-in, and for anyone who wants to understand how it works (including a marketplace certification team).
2. Prerequisites
| Area | Requirement |
|---|---|
| Administrator | Exchange administrator or Global administrator role on the tenant |
| Licensing | Microsoft 365 Business (Basic/Standard/Premium) or Enterprise (E1/E3/E5/F3), with Exchange Online mailboxes (the add-in does not support on-premises Exchange) |
| Subscription | An active ATOM Signature subscription (accessing the console and getting the deployment URL requires no prior installation) |
3. Step 1 — Get the deployment URL
In the ATOM Signature console (/app), open the Connections tab and generate your organization's manifest URL. This URL embeds a token unique to your organization, which lets the deployed add-in fetch the right signatures. Copy it — it is shown only once.
4. Step 2 — Deploy through the Microsoft 365 admin center
- Open admin.cloud.microsoft → Settings → Integrated apps.
- Select Upload custom apps.
- Choose the app type "Office Add-in" (not "Teams app").
- Select "Provide link to manifest file" and paste the URL obtained in the previous step, then validate.
- Choose the assignment: everyone (recommended — fine-grained signature targeting is then handled by groups in the console), or specific users and groups.
- Click Deploy and accept the permissions summary.
Administrators comfortable with PowerShell can use Microsoft's official O365CentralizedAddInDeployment module instead of the web interface — the result is identical.
5. Supported Outlook clients
Once deployed, the add-in automatically applies on:
- Outlook on the web;
- the new Outlook for Windows;
- classic Outlook for Windows (recent Microsoft 365 builds);
- Outlook for Mac;
- Outlook mobile (iOS and Android), with an organization Microsoft 365 account.
No separate configuration is needed per platform: a single deployment covers all of them.
6. Propagation delay and verification
Microsoft states that a new deployment can take up to 24 hours to propagate (up to 72 hours on mobile), often much less in practice. This delay is imposed by Microsoft, not by ATOM Signature.
The most reliable proof that a deployment is working isn't the admin center screen, but the signal received by the service when a mailbox composes a message: in the console, Connections tab, the add-in's status switches to "Active". To test: compose a new message in Outlook on the web — the signature should insert itself, with no button or window.
7. The add-in doesn't show up — what to do
- Allow for the propagation delay described above before concluding there's a problem.
- In Outlook on the web, sign out completely and sign back in (a simple refresh is not enough).
- In desktop Outlook, fully restart the application.
- In the admin center, check that the deployment was assigned to the right users or groups.
- In the ATOM Signature console (Connections tab), check that the add-in status and the subscription are both active.
If the problem persists after these checks, see the support page or write to us.
8. Updating or removing the add-in
An add-in update is served automatically at the same manifest URL; to roll it out to your organization, go back to the admin center, open the add-in's card, and choose to update or redeploy it from the same URL. To remove the add-in, delete it from Integrated apps, or from the console's Connections tab.
9. Contact us
For any deployment question, write to info@atomsolutions.ca or see the support page.