How different are Gmail and Yahoo Mail?

They disagree on 100 of the 300 features verified in both clients, or 33%. 99 features render in both and are the safe intersection to build on.

What works in Gmail but not Yahoo Mail?

38 features, including , , , , [aria-hidden] and 33 more. Each needs a fallback if the send reaches both clients.

Which engines are these two clients using?

Gmail renders with Gmail Web; Yahoo Mail renders with Yahoo. Where two clients share an engine the divergence is usually configuration, and where they do not it is the engine itself.

Is this measured in the real clients?

No. These are documented support levels derived from caniemail.com (MIT-licensed), carried in @emailens/engine data version 0.18.22 and last synced Nov 10, 2026. That sync date is not a test date: caniemail's own per-feature tests run from Feb 28, 2019 to Sep 16, 2026. Anything described as a transform is applied per those documented rules rather than captured from a real client.

Gmail vs Yahoo Mail: CSS Support Differences

Gmail renders with Gmail Web; Yahoo Mail renders with Yahoo. Both clients break features the other renders, on 33% of the 300 features verified in both. There is no "stricter" client here to build against, so the safe set is the 99-feature intersection.

Support data derived from caniemail.com (MIT) - last synced Nov 10, 2026 - engine data v0.18.22

work in both

the safe intersection

only in Gmail

breaks in Yahoo Mail

only in Yahoo Mail

breaks in Gmail

partial on one side

renders, with caveats

Works in Gmail, breaks in Yahoo Mail

Each of these needs a fallback if the send reaches both.

Partial on one side

These render in both, but one client applies caveats the other does not. They fail quietly, which makes them the expensive ones.

A further 101 features render in neither client. Not a difference between them, but the other half of the answer to what you can actually use, so the four counts above deliberately do not sum to 300.

Where the divergence sits

Two pairs with the same headline number can be different problems. For these two it concentrates in CSS Properties.

CSS Properties 50
Pseudo-Classes & Selectors 16
HTML Elements 12
CSS Functions 7
HTML Attributes 5
CSS At-Rules 4

15 of these already have a fix

Each links to a copy-paste snippet that keeps the feature working in Yahoo Mail without dropping it in Gmail.

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Questions

How different are Gmail and Yahoo Mail?: They disagree on 100 of the 300 features verified in both clients, or 33%. 99 features render in both and are the safe intersection to build on.
What works in Gmail but not Yahoo Mail?: 38 features, including <abbr>, <acronym>, <button type="reset">, <form>, [aria-hidden] and 33 more. Each needs a fallback if the send reaches both clients.
Which engines are these two clients using?: Gmail renders with Gmail Web; Yahoo Mail renders with Yahoo. Where two clients share an engine the divergence is usually configuration, and where they do not it is the engine itself.
Is this measured in the real clients?: No. These are documented support levels derived from caniemail.com (MIT-licensed), carried in @emailens/engine data version 0.18.22 and last synced Nov 10, 2026. That sync date is not a test date: caniemail's own per-feature tests run from Feb 28, 2019 to Sep 16, 2026. Anything described as a transform is applied per those documented rules rather than captured from a real client.

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