Outlook add-in

Outlook add-in (/admin/outlook) is where your organisation's add-in comes from. Deploy the Outlook add-in walks through putting it in front of everyone from the Microsoft 365 admin center.

Before it exists

Create the Outlook add-in issues your organisation's add-in key and its manifest. The screen also says where the add-in works and what it sees, so you can check both before you deploy it.

Your manifest

• Manifest URL, with Copy URL, and Download manifest for uploading the file instead. The URL carries your add-in key: treat it like a password for your signatures, because anyone who has it can read them.
• When the key was issued.
• Whether it is in use: Not seen yet until Microsoft has deployed it (up to 24 hours) and someone writes a message; then how many people it served a signature to in the last 30 days. Each of them shows as Outlook add-in on People, which counts as signing.

Creating the add-in also tells the Setup guide that nobody needs an invitation for their mail to be signed, so its step Invite your team becomes optional.

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. If you also use the relay, mail the add-in signed is marked, and the relay passes it through instead of adding a second signature.

What the add-in sees

While someone writes, 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.

Rotate the key

Rotate key issues a new manifest URL and stops the old one at once. Outlook inserts no signatures until you upload the new manifest in the Microsoft 365 admin center, so only rotate when the link went somewhere it should not have.