Apple Mail does not offer creation of email signatures from HTML. Only a rich-text editing box is provided, without the ability for more customization.
HTML Email Signature - Mail enhances these capabilities by allowing customized creation of email signatures from HTML. Simply add your HTML, and...
What's new in version 1.9.3
- Enhanced image preview error reporting with detailed alerts for CORS issues and missing images - Warnings for use of additional, non-recommended HTML tags - Guided walkthrough for folder selection in dialog (for troubleshooting)