Feature Announcement · Protocol

The spread is what matters on this template: 100 in Superhuman against 73 in Outlook Classic, a 27-point gap across the same file. 5 of the 21 clients render it without a single flagged property. Outlook Classic is the one to preview against after any edit, because it is where this template has the least margin, and the 217 warnings behind that score are concentrated there rather than spread evenly.

At 24.3KB compiled it has roughly 78KB of headroom before Gmail clips the message at 102KB and hides the rest behind a "View entire message" link. Inlined CSS and base64 images both count toward that, so watch it as you add sections.

Safe to customise. The screenshots and the walkthrough copy. This is the longest thing most products send, which makes total size the constraint to watch rather than layout.

Leave alone. The heading hierarchy. It carries the outline screen readers announce, and flattening headings into styled text is the most common accessibility regression in announcement mail.

Modified it? Check your version against the same 21 clients. The score above is computed from this file, so it moves when the file does.

Scores are computed by the Emailens engine from per-client support data derived from caniemail.com (MIT), analysed against 21 clients and last verified 2026-09-02.