Outlook for Windows — classic (Microsoft 365 / Office 2019/2021)

1. Open Outlook → File → Options → Mail → Signatures…

2. Click New, name your signature, and paste/type your content. Use Insert Picture to add a logo.

3. Under Choose default signature, select your E‑mail account, then pick the signature for New messages and Replies/forwards.

4. While composing, you can switch signatures via Message tab → Signature.

Tip: Outlook respects inline styles best; avoid external CSS and fancy fonts.

Outlook for Windows — New Outlook (the web‑style app)

1. Click the gear icon (Settings) → Mail → Compose and reply.

2. In Email signature, create or paste your signature.

3. Turn on Automatically include my signature for New messages and/or Replies/forwards (per account if you have multiple).

4. In a message, you can still insert/switch via the Signature button.

Outlook for Mac

1. Open Outlook → Settings/Preferences → Signatures.

2. Click + to add a signature and edit it in the right pane.

3. Assign defaults for New messages and Replies/forwards (per account).

4. While composing, use the Signature menu in the toolbar to switch.