Outlook for Mac email CSS: what breaks, and what to write instead

170 of 300 features work in Outlook for Mac · 37 partial · 92 not supported · 1 untested. Its closest client, Outlook (New), agrees on 279 of the 299 features both are tested on.

Works 170 · Partial 37 · Not supported 92 · Untested 1 · of 300

WebKit · desktop · prefers-color-scheme: works

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@emailens/engine 0.18.22 · data last changed 10 Nov 2026

Where Outlook for Mac is the outlier

2 features work in at least 14 of the other 20 clients and are not supported here.

So an email that looks right in most clients can reach your reader in Outlook for Mac without them.

What to write instead

8 features Outlook for Mac does not fully support have a written fix. See them in the table ↓

border-spacing

The fix for Outlook for Mac

Use the cellspacing HTML attribute instead of border-spacing CSS

after

3 lines

<table cellspacing="8" style="border-collapse: separate;">
  <tr><td>Cell</td></tr>
</table>

Show the original

before

3 lines

<table style="border-spacing: 8px; border-collapse: separate;">
  <tr><td>Cell</td></tr>
</table>

Test this fix, free

Outlook for Mac opens with a free account; the checker shows five clients without one.

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text-shadow

The fix for Outlook for Mac

Use font-weight or border-bottom as alternatives to text-shadow

after

6 lines

.glow {
  /* text-shadow is not supported in Gmail, Outlook, Yahoo.
     Use font-weight or letter-spacing for emphasis instead. */
  font-weight: bold;
  letter-spacing: 0.5px;
}

Show the original

before

3 lines

.glow {
  text-shadow: 0 0 10px rgba(255, 255, 255, 0.5);
}

Test this fix, free

Outlook for Mac opens with a free account; the checker shows five clients without one.

The checker needs a computer screen.

transform

The fix for Outlook for Mac

Pre-render transformed states as images or use table layout

The engine still flags this in the fix: An image points to an address no inbox can load (rotated-content.png), so Outlook for Mac shows a broken image instead.

after

4 lines

<!-- Pre-render rotated content as an image -->
<img src="rotated-content.png" width="200" height="200"
  alt="Rotated content"
  style="display: block; border: 0;" />

Show the original

before

3 lines

<div style="transform: rotate(45deg);">
  Rotated content
</div>

Test this fix, free

Outlook for Mac opens with a free account; the checker shows five clients without one.

The checker needs a computer screen.

Paste your email and see what Outlook for Mac does to it.

Check your email, free

No signup · Five clients free, Outlook Classic included · All 21 with an account

The checker needs a computer screen.

Dark mode in Outlook for Mac

Works @media prefers-color-scheme works in Outlook for Mac.

Works in 9 of 21.
Not supported color-scheme is not supported in Outlook for Mac.

Works in 4 of 21.
Not supported meta-color-scheme is not supported in Outlook for Mac.

Works in 2 of 21.

How to target Outlook for Mac

Selectors that single out Outlook for Mac, from the community list the engine ships (howtotarget.email). Copy one and replace .your-class-name.

css

3 lines

#converted-body .your-class-name {
  /* Replace this comment with your styles */
}

Build one for several clients →

Before you send to Outlook for Mac

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Outlook (New) · Outlook Classic · Apple Mail · Thunderbird · Superhuman

Every feature in Outlook for Mac

What breaks here (129) Everything (300) Untested (1)

HTML Elements · 15 of 48 not supported or partial here

<abbr> Works Works in 14 of 21
<acronym> Works Works in 13 of 21
<address> Works Works in 20 of 21
<audio> Not supported Works in 4 of 21
<base> Buggy. Partial Works in 4 of 21
<bdi> Not supported Works in 6 of 21
<blockquote> Works Works in 19 of 21
<body> Not supported Works in 5 of 21
<button type="reset"> Works Works in 10 of 21
<button type="submit"> Not supported Works in 11 of 21
<code> Works Works in 20 of 21
<del> Works Works in 20 of 21
<dfn> Works Works in 17 of 21
<dialog> Not supported Works in 5 of 21
<div> Works Works in 20 of 21
<form> fix Not supported. Partial Works in 10 of 21
<h1> Works Works in 20 of 21
<hr> Works Works in 18 of 21
<img> Works Works in 19 of 21
<input type="checkbox"> Works Works in 16 of 21
<input type="hidden"> Works Works in 16 of 21
<input type="radio"> Works Works in 16 of 21
<input type="reset"> Works Works in 15 of 21
<input type="submit"> Not supported Works in 12 of 21
<input type="text"> Works Works in 13 of 21
<link> fix Not supported Works in 3 of 21
<marquee> The <marquee> element is supported but not the behavior or direction attributes. Partial Works in 8 of 21
<meter> Works Works in 11 of 21
<object> Not supported Works in 1 of 21
<p> Works Works in 20 of 21
<picture> Not supported Works in 4 of 21
<pre> Works Works in 20 of 21
<progress> Not supported Works in 6 of 21
<rp> Works Works in 15 of 21
<rt> Works Works in 15 of 21
<ruby> Works Works in 15 of 21
<select> Works Works in 14 of 21
<small> Works Works in 20 of 21
<span> Works Works in 20 of 21
<strike> Works Works in 17 of 21
<strong> Works Works in 20 of 21
<style> Works Works in 16 of 21
<svg> fix Not supported Works in 5 of 21
<table> Works Works in 20 of 21
<textarea> Works Works in 13 of 21
<ul> Partial. Partial Works in 7 of 21
<video> Works Works in 3 of 21
<wbr> Works Works in 16 of 21

HTML Attributes · 9 of 22 not supported or partial here

[align] Partial. Partial Works in 17 of 21
[aria-describedby] Works Works in 9 of 21
[aria-hidden] Works Works in 13 of 21
[aria-label] Works Works in 13 of 21
[aria-labelledby] Works Works in 7 of 21
[aria-live] Not supported Works in 8 of 21
[background] Works Works in 16 of 21
[cellpadding] Works Works in 18 of 21
[cellspacing] Works Works in 18 of 21
[command] Not supported Works in 3 of 21
[dir] Works Works in 19 of 21
[height] Works Works in 18 of 21
[hidden] Not supported Works in 5 of 21
[lang] Works Works in 15 of 21
[loading] Not supported Works in 4 of 21
[popover] Not supported Works in 3 of 21
[required] Not supported Works in 7 of 21
[role] Works Works in 14 of 21
[srcset] Not supported Works in 4 of 21
[target] The attribute is supported but links always open in a new window anyway. Partial Works in 0 of 21
[valign] Works Works in 20 of 21
[width] Works Works in 18 of 21

HTML & Email Structure · 3 of 8 not supported or partial here

amp4email Not supported Works in 6 of 21
anchor-links Works Works in 12 of 21
doctype Works Works in 13 of 21
html-comments Works Works in 18 of 21
html5-semantics Partial. Partial Works in 6 of 21
image-maps Works Works in 15 of 21
mailto-links Works Works in 17 of 21
meta-color-scheme Not supported Works in 2 of 21

CSS At-Rules · 5 of 10 not supported or partial here

@font-face Not supported Works in 6 of 21
@import Not supported Works in 4 of 21
@keyframes Not supported Works in 7 of 21
@media Partial. Partial Works in 5 of 21
@media device-pixel-ratio Works Works in 10 of 21
@media hover Works Works in 9 of 21
@media orientation Works Works in 11 of 21
@media prefers-color-scheme Works Works in 9 of 21
@media prefers-reduced-motion Works Works in 9 of 21
@supports Not supported Works in 9 of 21

Pseudo-Elements · 6 of 6 not supported or partial here

::after Not supported with non Outlook accounts. Partial Works in 6 of 21
::before Not supported with non Outlook accounts. Partial Works in 6 of 21
::first-letter Not supported with non Outlook accounts. Partial Works in 10 of 21
::first-line Not supported with non Outlook accounts. Partial Works in 10 of 21
::marker Not supported Works in 10 of 21
::placeholder Not supported with non Outlook accounts. Partial Works in 9 of 21

Pseudo-Classes & Selectors · 23 of 34 not supported or partial here

:adjacent-sibling Works Works in 16 of 21
:attribute-selector Partial. Partial Works in 6 of 21
:chaining Works Works in 14 of 21
:checked Partial. Partial Works in 9 of 21
:child-combinator Works Works in 16 of 21
:class-selector Works Works in 17 of 21
:descendant-combinator Works Works in 17 of 21
:first-child Partial. Partial Works in 12 of 21
:first-of-type Partial. Partial Works in 12 of 21
:focus Partial. Partial Works in 10 of 21
:focus-visible Partial. Partial Works in 6 of 21
:focus-within Partial. Partial Works in 6 of 21
:general-sibling Works Works in 16 of 21
:grouping Works Works in 17 of 21
:has Not supported Works in 5 of 21
:hover Partial. Partial Works in 12 of 21
:id-selector Works Works in 17 of 21
:lang Not supported Works in 6 of 21
:last-child Partial. Partial Works in 12 of 21
:last-of-type Partial. Partial Works in 12 of 21
:link Partial Works in 13 of 21
:not Not supported Works in 6 of 21
:nth-child Not supported Works in 6 of 21
:nth-last-child Not supported Works in 6 of 21
:nth-of-type Not supported Works in 6 of 21
:only-child Partial. Partial Works in 12 of 21
:only-of-type Partial. Partial Works in 12 of 21
:target Partial. Partial Works in 7 of 21
:type-selector Works Works in 17 of 21
:universal-selector Works Works in 16 of 21
:visited Partial. Partial Works in 8 of 21
pseudo-class-active Partial. Partial Works in 8 of 21
pseudo-class-default Works Works in 10 of 21
pseudo-class-nth-last-of-type Not supported Works in 6 of 21

CSS Functions · 7 of 8 not supported or partial here

calc Not supported Works in 8 of 21
clamp Not supported Works in 6 of 21
conic-gradient Not supported Works in 6 of 21
fit-content Works Works in 11 of 21
linear-gradient Not supported Works in 9 of 21
max Not supported Works in 6 of 21
min Not supported Works in 6 of 21
radial-gradient Not supported Works in 10 of 21

CSS Properties · 61 of 164 not supported or partial here

!important Works Works in 11 of 21
accent-color Not supported Works in 5 of 21
align-items Works Works in 13 of 21
animation fix Not supported Works in 5 of 21
aspect-ratio Not supported Works in 5 of 21
backdrop-filter Works Works in 6 of 21
background Works Works in 16 of 21
background-blend-mode Works Works in 13 of 21
background-clip Works Works in 14 of 21
background-color Works Works in 21 of 21
background-image Works Works in 16 of 21
background-origin Works Works in 14 of 21
background-position Works Works in 20 of 21
background-repeat Works Works in 20 of 21
background-size Works Works in 17 of 21
bimi Not supported Works in 9 of 21
block-size Not supported Works in 7 of 21
border Works Works in 20 of 21
border-collapse Works Works in 19 of 21
border-image Not supported Works in 7 of 21
border-inline Not supported Works in 3 of 21
border-inline-individual Not supported Works in 3 of 21
border-inline-longhand Not supported Works in 4 of 21
border-radius Works Works in 16 of 21
border-radius-logical Not supported Works in 3 of 21
border-spacing fix Not supported Works in 17 of 21
bottom Works Works in 11 of 21
box-shadow Works Works in 14 of 21
box-sizing Works Works in 16 of 21
caption-side Works Works in 20 of 21
clear Untested Works in 9 of 21
clip-path Not supported Works in 8 of 21
color Works Works in 21 of 21
color-scheme Not supported Works in 4 of 21
column-count Works Works in 16 of 21
columns Works Works in 16 of 21
css-comments Works Works in 14 of 21
cursor Not supported Works in 2 of 21
custom-properties Not supported Works in 6 of 21
direction Works Works in 21 of 21
display Works Works in 13 of 21
display:flex Works Works in 18 of 21
display:grid Works Works in 18 of 21
display:none Works Works in 20 of 21
empty-cells Works Works in 14 of 21
filter Not supported Works in 7 of 21
flex Works Works in 13 of 21
flex-basis Works Works in 13 of 21
flex-direction Works Works in 12 of 21
flex-wrap Works Works in 13 of 21
float Works Works in 14 of 21
font Works Works in 20 of 21
font-family Works Works in 21 of 21
font-kerning Works Works in 13 of 21
font-size Works Works in 13 of 21
font-size-adjust Works Works in 10 of 21
font-stretch Works Works in 10 of 21
font-weight Works Works in 16 of 21
gap Partial. Partial Works in 7 of 21
grid-template-columns Observed 2026-10-27 (Emailens probe sheets 20-22, the new Outlook for Mac): Plain track sizes work (300px 300px, 1fr 1fr); a value with repeat() or minmax() is dropped, so the grid falls back to one column. Partial Works in 7 of 21
height Works Works in 16 of 21
hyphenate-character Not supported Works in 4 of 21
hyphenate-limit-chars Not supported Works in 1 of 21
hyphens Not supported Works in 4 of 21
inert Not supported Works in 3 of 21
inline-size Not supported Works in 4 of 21
inset Not supported Works in 3 of 21
justify-content Works Works in 13 of 21
left Works Works in 11 of 21
letter-spacing Works Works in 20 of 21
light-dark Not supported Works in 3 of 21
line-height Works Works in 20 of 21
list-style list-style-image values are not supported but the rest of the list-style property is kept. Partial Works in 11 of 21
list-style-image Not supported Works in 6 of 21
list-style-position Works Works in 19 of 21
list-style-type Works Works in 21 of 21
margin Partial. Partial Works in 8 of 21
margin-block-start-end Not supported Works in 4 of 21
margin-inline-block Not supported Works in 6 of 21
margin-inline-start-end Not supported Works in 4 of 21
mask-image Works Works in 4 of 21
max-block-size Not supported Works in 5 of 21
max-height Works Works in 20 of 21
max-inline-size Not supported Works in 4 of 21
max-width Works Works in 20 of 21
min-block-size Not supported Works in 4 of 21
min-height Works Works in 19 of 21
min-inline-size Not supported Works in 5 of 21
min-width Works Works in 20 of 21
mix-blend-mode Works Works in 13 of 21
modern-color Not supported Works in 4 of 21
nesting Not supported Works in 2 of 21
object-fit Works Works in 14 of 21
object-position Works Works in 14 of 21
opacity Works Works in 19 of 21
orphans Works Works in 10 of 21
outline Works Works in 20 of 21
outline-offset Not supported Works in 7 of 21
overflow Partial. Partial Works in 4 of 21
overflow-wrap fix Not supported Works in 2 of 21
padding Works Works in 20 of 21
padding-block-start-end Not supported Works in 4 of 21
padding-inline-block Not supported Works in 3 of 21
padding-inline-start-end Not supported Works in 4 of 21
position Partial. Partial Works in 2 of 21
resize resize property is stripped from style tag Not supported Works in 1 of 21
rgb Works Works in 12 of 21
rgba Works Works in 12 of 21
right Works Works in 11 of 21
scroll-snap Not supported Works in 6 of 21
shape-margin Works Works in 6 of 21
shape-outside Works Works in 6 of 21
system-ui Works Works in 12 of 21
tab-size Works Works in 8 of 21
table-layout Not supported. Not supported Works in 16 of 21
text-align Works Works in 13 of 21
text-align-last Not supported Works in 7 of 21
text-decoration Observed 2026-10-14 (Emailens real-device probe, Outlook 2019 for Mac (legacy app)): The multi-value shorthand text-decoration: underline wavy #d33 was dropped whole: no line at all. Partial Works in 14 of 21
text-decoration-color Works Works in 17 of 21
text-decoration-line Works Works in 16 of 21
text-decoration-skip-ink Not supported Works in 7 of 21
text-decoration-style Works Works in 16 of 21
text-decoration-thickness Not supported Works in 7 of 21
text-emphasis Works Works in 9 of 21
text-emphasis-position Works Works in 4 of 21
text-indent Works Works in 13 of 21
text-justify Buggy. Not supported Works in 0 of 21
text-orientation Works Works in 13 of 21
text-overflow Works Works in 13 of 21
text-shadow fix Not supported Works in 12 of 21
text-transform Works Works in 20 of 21
text-underline-offset Not supported Works in 7 of 21
text-underline-position Not supported Works in 8 of 21
text-wrap Not supported Works in 4 of 21
top Works Works in 11 of 21
transform fix Not supported Works in 7 of 21
transition Not supported Works in 4 of 21
unit-ch Works Works in 15 of 21
unit-cm Works Works in 20 of 21
unit-em Works Works in 20 of 21
unit-ex Works Works in 20 of 21
unit-in Works Works in 20 of 21
unit-initial Works Works in 12 of 21
unit-mm Works Works in 20 of 21
unit-pc Works Works in 20 of 21
unit-percent Works Works in 20 of 21
unit-pt Works Works in 20 of 21
unit-px Works Works in 20 of 21
unit-rem Works Works in 15 of 21
unit-vh Works Works in 17 of 21
unit-vmax Works Works in 15 of 21
unit-vmin Works Works in 15 of 21
unit-vw Works Works in 18 of 21
user-select Property is stripped from style tag Not supported Works in 3 of 21
vertical-align Works Works in 21 of 21
visibility Works Works in 13 of 21
white-space Works Works in 15 of 21
white-space-collapse Not supported Works in 4 of 21
widows Works Works in 10 of 21
width Works Works in 20 of 21
word-break Buggy. Partial Works in 4 of 21
word-spacing Works Works in 14 of 21
writing-mode Works Works in 13 of 21
z-index Works Works in 17 of 21