border

Client-by-client behaviour for border

Fully supports border (13): Gmail, Gmail Android, Gmail iOS, Outlook 365, Outlook iOS, Outlook Android, Apple Mail, Apple Mail iOS, Yahoo Mail, Samsung Mail, Thunderbird, HEY Mail, Superhuman.

Partial support (2): Outlook (New), Outlook Classic. Expect rendering quirks unique to each engine — partial support typically means a subset of values, an ignored shorthand, or sanitizer-specific rewrites.

When to use border in email

• Drawing dividers between sections in a digest email by setting border-bottom on a <td>.
• Outlining promotional cards with a colored stroke that ties into brand identity.
• Highlighting CTA buttons with a contrasting border that survives image-blocking.

Rendering behaviour and edge cases

• Outlook on Windows occasionally renders an unstyled <table> with default 1px borders — explicitly set border="0" cellspacing="0" cellpadding="0" on every layout table.
• Apple Mail and Gmail support all border styles (dashed, dotted, double) but render them at slightly different pixel widths.
• border on inline elements can be stripped by Yahoo's sanitizer — use a wrapping <span> with display:inline-block when targeting Yahoo.

Recommended fallback strategy

Always reset table defaults with border="0" cellspacing="0" cellpadding="0". Apply border on <td> rather than <table> for consistent rendering. For decorative borders, prefer a colored cell background over a thin border, since cell color is more reliably preserved than 1px lines.

Fixes & Workarounds