How different are Gmail and Apple Mail?

They disagree on 145 of the 298 features verified in both clients, or 49%. 149 features render in both and are the safe intersection to build on.

What works in Gmail but not Apple Mail?

1 features, including amp4email. Each needs a fallback if the send reaches both clients.

Which engines are these two clients using?

Gmail renders with Gmail Web; Apple Mail renders with WebKit. 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 0.12.2 and last synced Sep 2, 2026. That sync date is not a test date: caniemail's own per-feature tests run from Feb 28, 2019 to Jul 13, 2026. Anything described as a transform is applied per those documented rules rather than captured from a real client.

Gmail vs Apple Mail: CSS Support Differences

Gmail renders with Gmail Web; Apple Mail renders with WebKit. The gap runs almost entirely one way: 115 features work in Apple Mail and break in the other, against 1 in the reverse direction. Build for the stricter one and the permissive one follows.

Support data derived from caniemail.com (MIT) - last synced Sep 2, 2026 - engine data v0.12.2

149

work in both

the safe intersection

only in Gmail

breaks in Apple Mail

115

only in Apple Mail

breaks in Gmail

partial on one side

renders, with caveats

Works in Gmail, breaks in Apple Mail

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

amp4email

Works in Apple Mail, breaks in Gmail

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 4 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 298.

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 78
Pseudo-Classes & Selectors 21
HTML Elements 18
HTML Attributes 9
CSS At-Rules 9
Pseudo-Elements 6

8 of these already have a fix

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

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Questions

How different are Gmail and Apple Mail?: They disagree on 145 of the 298 features verified in both clients, or 49%. 149 features render in both and are the safe intersection to build on.
What works in Gmail but not Apple Mail?: 1 features, including amp4email. Each needs a fallback if the send reaches both clients.
Which engines are these two clients using?: Gmail renders with Gmail Web; Apple Mail renders with WebKit. 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 0.12.2 and last synced Sep 2, 2026. That sync date is not a test date: caniemail's own per-feature tests run from Feb 28, 2019 to Jul 13, 2026. Anything described as a transform is applied per those documented rules rather than captured from a real client.

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