HTML Email
Published format-level guidance.
Required
Not specified by platform
Recommended
Not specified by platform
Placement-dependent
Not specified by platform
Cphere best practice
Not specified by platform
Marketing Email
Direct linkDeliverability requirements come from mailbox providers; visual conventions are industry guidance.
Required
- Message Format
- Format messages per RFC 5322; HTML must follow HTML standards; never hide content with HTML or CSS; links must be visible and predictable
- Unsubscribe
- Bulk senders (5,000+/day to Gmail) must support one-click unsubscribe (List-Unsubscribe headers) and a visible unsubscribe link
Recommended
Not specified by platform
Placement-dependent
Not specified by platform
Cphere best practice
- Body Width
- 600–640 pixels pixels — Industry convention (Litmus); not a platform mandate.
- Image Weight
- Individual images under 200 KB; total email assets around 1 MB or less — Industry convention (Litmus); not a platform mandate.
- Html Weight
- Keep the HTML under roughly 102 KB to avoid Gmail clipping — Observed Gmail behavior documented by industry sources; not stated in Google's official guidelines.
- Accessibility
- Alt text on all images; live text over image-only text; test light and dark mode with transparent-safe PNGs — Industry convention (Litmus).