Home · Install guides · Classic Outlook

Add your signature to classic Outlook

⏱ 1–2 minutes · The desktop Outlook with the File → Options menu (Microsoft 365 / Outlook 2016–2021)

Option A — quick paste

  1. In the OnceSig editor, click “Copy signature”.
  2. In Outlook, go to “File” → “Options” → “Mail” → “Signatures…”.
  3. Click “New”, name the signature, click “OK”.
  4. Click inside the editing box and paste with Ctrl+V.
  5. Set it under “New messages” and “Replies/forwards”, then click “OK”.
Heads up: classic Outlook's signature editor runs everything through Word, which can subtly re-format pasted HTML (spacing, image size). If your signature looks slightly off after pasting, use Option B — it bypasses the editor entirely.

Option B — install the .htm file (pixel-perfect)

  1. In the OnceSig editor, click “Download .htm” — you get a file named OnceSig.htm.
  2. Close Outlook.
  3. Press Win+R, type %APPDATA%\Microsoft\Signatures and press Enter.
  4. Move OnceSig.htm into that folder.
  5. Start Outlook, go to File → Options → Mail → Signatures — “OnceSig” now appears in the list.
  6. Assign it to “New messages” / “Replies/forwards” and click OK. Don’t edit it inside Outlook’s editor.
Why this works: Outlook reads signature files straight from that folder. Because the file was generated by OnceSig (tables, inline styles, Outlook-specific line-height rules), it renders exactly as previewed. Opening it in Outlook's signature editor re-saves it through Word and can mangle it — select it, assign it, leave it alone.

Good to know

Don't have your signature yet?

Build one free — then install it with the .htm file for a pixel-perfect result.

Open the OnceSig editor