Microsoft Outlook doesn’t have a built-in way to modify plain-text email signatures. They are automatically generated from the normal HTML signature by removing all formatting and images.

To edit plain text signatures:

• Navigate to: C:\Users\[username]\AppData\Roaming\Microsoft\Signatures folder.
• Open the .txt file with the signature’s name, make the required changes and save it back.

This is it, the modified signature will be applied to all plain-text emails. However, any time you edit your signature via Outlook GUI, this file will be overwritten.

December 2023
Windows 11 Pro
MS Outlook 365