How to add a signature in Outlook
Outlook on the web: Settings → Accounts → Signatures. Create a signature, paste into the editor, and assign it to new messages. Desktop Outlook (Windows or Mac): File → Options → Mail → Signatures, or Outlook → Settings → Signatures on Mac. Paste the HTML. If the paste lands as raw tags, paste into a blank message first, copy the formatted result, then paste that into the signature editor.
Some corporate tenants strip external images. The free layout is text-first for that reason. A logo and social icons are on the Pro waitlist.