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box-sizing in Gmail iOS

Works box-sizing works in Gmail iOS.

Works in 16 of 21 · not supported in 5

Which clients
Works
Gmail, Gmail Android, Gmail iOS, Outlook 365, Outlook (New), Outlook iOS, Outlook Android, Outlook for Mac, Apple Mail, Apple Mail iOS, Samsung Mail, Thunderbird, HEY Mail, Proton Mail, Fastmail, Superhuman
Not supported
Outlook Classic, Yahoo Mail, Yahoo Mail Android, Yahoo Mail iOS, AOL Mail

The fix for the clients that need it

Needed in 5 of 21: Outlook Classic, Yahoo Mail, Yahoo Mail Android and 2 more.

Account for padding in width manually (no box-sizing)

instead 
<div style="width: 300px;">
  <div style="padding: 20px;">
    Content; padding on inner element
  </div>
</div>
Show the original
before 
<div style="width: 300px; padding: 20px;
            box-sizing: border-box;">
  Content; total width stays 300px
</div>

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Your next question

Every feature in Gmail iOS · box-sizing in every client

Questions

How many email clients support box-sizing?
It works in 16 of 21, not supported in 5.
Does box-sizing work in Gmail Android?
box-sizing works in Gmail Android. Closest to Gmail iOS: Gmail Android, which agrees on 273 of the 300 features both are tested on.

To see what in your email Gmail iOS does not support, paste the whole email.

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Real captures 14 Oct 2026 on 11 installs · caniemail (MIT) via @emailens/engine 0.18.22 · tested upstream 28 Feb 2019 · data last changed 10 Nov 2026 · Outlook (New) cells are the engine's mapping · the Gmail capture is not counted (it skips Gmail's sanitiser)