box-sizing in Outlook Classic
Not supported box-sizing is not supported in Outlook Classic.
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
Your reader in Outlook Classic sees the email without box-sizing, even if it looks right where you tested it.
What to do instead in Outlook Classic
Account for padding in width manually (no box-sizing)
<div style="width: 300px;">
<div style="padding: 20px;">
Content; padding on inner element
</div>
</div>Show the original
<div style="width: 300px; padding: 20px;
box-sizing: border-box;">
Content; total width stays 300px
</div>A free account opens all 21 clients and keeps your checks for 7 days. Create a free account →
What Outlook Classic does with box-sizing
The Emailens probe for box-sizing on 3 real installs counted as Outlook Classic, captured 14 Oct 2026. It shows the problem, not the fix. Where box-sizing is supported it shows: both bars the same width.
caniemail: box-sizing is not supported in Outlook Classic.
Every account includes one free real-device check in classic Outlook, Outlook for Mac and Apple Mail, after you verify your email and run one preview, while this month's free capacity lasts. How real-device checks work →
@emailens/engine 0.18.22 on the original code
Outlook Classic does not support "box-sizing".
Your next question
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Works in 4 of 21 · partial in 12 · not supported in 5
fix - Does display:flex work in Outlook Classic?
Works in 18 of 21 · partial in 2 · not supported in 1
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Works in 13 of 21 · not supported in 8
fix
Every feature in Outlook Classic · box-sizing in every client
Questions
- How many email clients support box-sizing?
- It works in 16 of 21, not supported in 5.
- What do I use instead of box-sizing in Outlook Classic?
- Account for padding in width manually (no box-sizing).
- Does box-sizing work in AOL Mail?
- box-sizing is not supported in AOL Mail. Closest to Outlook Classic: AOL Mail, which agrees on 206 of the 298 features both are tested on.
To see what else in your email Outlook Classic does not support, paste the whole email.
No signup · Five clients free, Outlook Classic included · All 21 with an account
The checker needs a computer screen.
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