Apple Mail is quietly the strictest email client. Here's why we love it.
Apple Mail isn't quirky — it's actually the most standards-compliant. If your signature looks great in Apple Mail, your CSS is probably correct.
Tomás Reyes
· Senior front-end engineer ·
Apr 2, 2026
·
6 min read
The reputation
Apple Mail gets a bad rap for "weird rendering," but in our experience, it's usually the cleanest renderer we test.
What it actually does
Apple Mail respects modern CSS — `border-radius`, `box-shadow`, even `mask-image` in some cases. The "weirdness" people complain about is usually that it shows you what your CSS actually does, instead of silently swallowing it like Outlook.
Use it as your reference
When we build a signature, Apple Mail is one of the first clients we render in. If the design is right there, fixing it for the older clients is a tractable problem. If it's not right in Apple Mail, the design is wrong.
Written by Tomás Reyes
Senior front-end engineer · ProEmailSign
