Deploy the Outlook add-in

The Outlook add-in puts each person's signature into a new message, reply or forward as they start writing, kept up to date from your directory. You deploy it once for your Microsoft 365 organisation; nobody installs anything themselves. Deploying needs a Microsoft 365 Global Administrator or Exchange Administrator and takes about five minutes.

The add-in signs with what your directory says, so connect Microsoft Entra ID first, or fill People another way.

1. Create the add-in on signplume

On Outlook add-in (/admin/outlook), press Create the Outlook add-in. signplume issues a manifest URL that carries your organisation's add-in key. Treat it like a password for your signatures: anyone who has it can read them.

2. Deploy it from the Microsoft 365 admin center

1. Open the Microsoft 365 admin center and go to Settings → Integrated apps.
2. Choose Upload custom apps, and as the app type pick Office Add-in.
3. Select Provide link to the manifest file, paste the manifest URL from signplume, and choose Validate. You can instead press Download manifest on signplume and upload the file.
4. Assign it to Entire organization, or to the people or group who should get signatures, and finish with Deploy.

Microsoft says a newly deployed add-in can take up to 24 hours to reach every mailbox.

Where it works

• Outlook on the web, the new Outlook for Windows, and classic Outlook for Windows and Mac on a current Microsoft 365 build.
• Not in Outlook 2016 or Outlook 2019. People on those can copy and paste their signature instead.

Once it is deployed

• The signature appears in each new message, reply, forward and meeting invite. The add-in turns off the signature people had set in Outlook, so it is not added twice.
• Directory changes apply from the next message: the signature is fetched each time, so nothing needs redeploying.
• Recipient rules apply, because the add-in tells signplume who the message is going to. People can switch between signature variants per message.
• On People, everyone the add-in served a signature to in the last 30 days shows as Outlook add-in in the Signing column, which counts as signing. The Outlook add-in screen counts them too.

What the add-in sees

While someone writes a message, the add-in sends signplume the sender and the To and Cc addresses, so it can pick the right template. It never reads the subject or the body, and it never sends anything: the person still presses Send.

If the manifest URL leaks

Rotate the key on Outlook add-in. The old URL stops working at once, and Outlook inserts no signatures until you upload the new manifest in the Microsoft 365 admin center, so only do this when the link went somewhere it should not have.