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Technical
HTML Email Signatures: A Technical Guide
November 14, 2025 7 min read
Marcus Rodriguez
Head of Product & Engineering at Siggly
Building HTML email signatures requires different techniques than web development. Here's what you need to know.
Key Principles
- Tables for layout — CSS flexbox/grid don't work reliably
- Inline styles — External CSS is stripped by most clients
- Absolute URLs — All images must use full URLs
- Simple HTML — Avoid divs, use basic elements
Email Client Challenges
- Outlook uses Word's rendering engine
- Gmail strips certain CSS properties
- Apple Mail is most forgiving
- Mobile clients have limited width
Safe CSS Properties
- color, font-family, font-size
- text-align, text-decoration
- padding (on table cells)
- border (on tables)
- width, height (on images)
What to Avoid
- CSS floats and positioning
- Background images (poor support)
- Web fonts (use font stacks)
- JavaScript (never works)
Tip: Using a signature management tool like Siggly handles all these technical complexities for you.