What is “bulletproof button” design?

A bulletproof button is a CTA button coded to render consistently across all email clients, including Outlook, without relying on images. It uses HTML and CSS (and VML for Outlook) to create styled buttons that work everywhere.

Why it matters: image-based buttons fail when images are blocked. CSS-only buttons break in Outlook. Bulletproof buttons use a combination: HTML table structure for Outlook compatibility, CSS styling for modern clients, VML background for rounded corners in Outlook, and live text that's always readable.

Every CTA should be bulletproof. Your most important element. The uaction you want recipients to take-must work for everyone. Use generators like buttons.cm to create compatible code. Test in Outlook specifically. A beautiful button that renders as plain text link in Outlook loses clicks from a significant audience segment.