CSS Properties

background-size

CSS property · 17 supported, 2 partial, 2 unsupported across 21 clients

17 of 21 email clients render background-size fully (Sep 2, 2026 data); it breaks outright in Outlook (New), Outlook Classic.

7/7 webmail, 4/6 desktop, 6/8 mobile clients support background-size fully.
Unsupported in Outlook (New), Outlook Classic.
Partial in Gmail Android, Gmail iOS, behavior differs from browsers, test before relying on it.
Outlook Classic (Word engine, supported to at least 2029) does not fully support background-size, and its replacement changes little here; see the deprecation diff.
Documented before/after fixes on this page cover 21 clients, including Gmail and Gmail Android.
Across all clients, only 6 of 298 tracked HTML/CSS features render identically everywhere.

Source: caniemail.com (MIT), via the Emailens engine. Last tested upstream Feb 28, 2019, synced by Emailens Sep 2, 2026.

Client Support

Client	Category	Engine	Support
Gmail	webmail	Gmail Web	Supported
Gmail Android	mobile	Gmail Mobile	Partial^{See caveat 1}
Gmail iOS	mobile	Gmail Mobile	Partial^{See caveat 1}
Outlook 365	webmail	Outlook Web	Supported
Outlook (New)	desktop	Outlook Web	Unsupported^{See caveat 2}
Outlook Classic	desktop	Microsoft Word	Unsupported
Outlook iOS	mobile	Outlook Mobile	Supported
Outlook Android	mobile	Outlook Mobile	Supported
Outlook for Mac	desktop	WebKit	Supported
Apple Mail	desktop	WebKit	Supported
Apple Mail iOS	mobile	WebKit	Supported
Yahoo Mail	webmail	Yahoo	Supported^{See caveat 3}
Yahoo Mail Android	mobile	Yahoo	Supported^{See caveat 3}
Yahoo Mail iOS	mobile	Yahoo	Supported^{See caveat 3}
Samsung Mail	mobile	Samsung	Supported
Thunderbird	desktop	Gecko	Supported
HEY Mail	webmail	WebKit	Supported
Proton Mail	webmail	Proton	Supported
AOL Mail	webmail	AOL	Supported^{See caveat 3}
Fastmail	webmail	Fastmail	Supported
Superhuman	desktop	Blink	Supported

Documented caveats (3)

1.Gmail Android, Gmail iOS: Partial. Not supported with non Google accounts. But it can be used in the background shorthand property instead.
2.Outlook (New): Background images size can be used in VML with the size attribute. See VML documentation.
3.Yahoo Mail, Yahoo Mail Android, Yahoo Mail iOS, AOL Mail: Partial. Does not support multiple values. The comma between two values is removed.

Caveats recorded by caniemail.com (MIT) and carried verbatim, one entry per wording rather than per client.

Client-by-client behaviour for background-size

Fully supports background-size (17): Gmail, Outlook 365, Outlook iOS, Outlook Android, Outlook for Mac, Apple Mail, Apple Mail iOS, Yahoo Mail, Yahoo Mail Android, Yahoo Mail iOS, Samsung Mail, Thunderbird, HEY Mail, Proton Mail, AOL Mail, Fastmail, Superhuman.

Partial support (2): Gmail Android, Gmail iOS. Expect rendering quirks unique to each engine. Partial support typically means a subset of values, an ignored shorthand, or sanitizer-specific rewrites.

No support (2): Outlook (New), Outlook Classic. Plan fallbacks for these clients before relying on background-size in production sends.

Fixes & Workarounds

Outlook (New)

Unsupported

Not supported in many clients. Set image dimensions directly.

Before (Broken)

before.html

3 lines

<td style="background: url('bg.jpg') center/cover no-repeat;">
  Content
</td>

After (Fixed)

fixed.html

15 lines

<td background="bg.jpg" bgcolor="#333333" width="600" height="400" valign="top"
    style="background-color: #333; background-image: url('bg.jpg');
           background-size: cover; background-position: center; background-repeat: no-repeat;">
  <!--[if gte mso 9]>
  <v:rect xmlns:v="urn:schemas-microsoft-com:vml" fill="true"
    stroke="false" style="width:600px; height:400px;">
    <v:fill type="frame" size="100%,100%" src="bg.jpg" color="#333333" />
    <v:textbox inset="0,0,0,0">
  <![endif]-->
  <div>Content</div>
  <!--[if gte mso 9]>
    </v:textbox>
  </v:rect>
  <![endif]-->
</td>

Outlook ignores background-size; use VML or sized images

Outlook Classic

Unsupported

Not supported in many clients. Set image dimensions directly.

Before (Broken)

before.html

3 lines

<td style="background: url('bg.jpg') center/cover no-repeat;">
  Content
</td>

After (Fixed)

fixed.html

15 lines

<td background="bg.jpg" bgcolor="#333333" width="600" height="400" valign="top"
    style="background-color: #333; background-image: url('bg.jpg');
           background-size: cover; background-position: center; background-repeat: no-repeat;">
  <!--[if gte mso 9]>
  <v:rect xmlns:v="urn:schemas-microsoft-com:vml" fill="true"
    stroke="false" style="width:600px; height:400px;">
    <v:fill type="frame" size="100%,100%" src="bg.jpg" color="#333333" />
    <v:textbox inset="0,0,0,0">
  <![endif]-->
  <div>Content</div>
  <!--[if gte mso 9]>
    </v:textbox>
  </v:rect>
  <![endif]-->
</td>

Outlook ignores background-size; use VML or sized images

Gmail Android

Partial

Not supported in many clients. Set image dimensions directly.

Before (Broken)

before.html

3 lines

<td style="background: url('bg.jpg') center/cover no-repeat;">
  Content
</td>

After (Fixed)

fixed.html

15 lines

<td background="bg.jpg" bgcolor="#333333" width="600" height="400" valign="top"
    style="background-color: #333; background-image: url('bg.jpg');
           background-size: cover; background-position: center; background-repeat: no-repeat;">
  <!--[if gte mso 9]>
  <v:rect xmlns:v="urn:schemas-microsoft-com:vml" fill="true"
    stroke="false" style="width:600px; height:400px;">
    <v:fill type="frame" size="100%,100%" src="bg.jpg" color="#333333" />
    <v:textbox inset="0,0,0,0">
  <![endif]-->
  <div>Content</div>
  <!--[if gte mso 9]>
    </v:textbox>
  </v:rect>
  <![endif]-->
</td>

Outlook ignores background-size; use VML or sized images

Gmail iOS

Partial

Not supported in many clients. Set image dimensions directly.

Before (Broken)

before.html

3 lines

<td style="background: url('bg.jpg') center/cover no-repeat;">
  Content
</td>

After (Fixed)

fixed.html

15 lines

<td background="bg.jpg" bgcolor="#333333" width="600" height="400" valign="top"
    style="background-color: #333; background-image: url('bg.jpg');
           background-size: cover; background-position: center; background-repeat: no-repeat;">
  <!--[if gte mso 9]>
  <v:rect xmlns:v="urn:schemas-microsoft-com:vml" fill="true"
    stroke="false" style="width:600px; height:400px;">
    <v:fill type="frame" size="100%,100%" src="bg.jpg" color="#333333" />
    <v:textbox inset="0,0,0,0">
  <![endif]-->
  <div>Content</div>
  <!--[if gte mso 9]>
    </v:textbox>
  </v:rect>
  <![endif]-->
</td>

Outlook ignores background-size; use VML or sized images

Production guidance for background-size

background-size is a CSS property. Across the email client matrix, 17 of 21 tracked clients support it fully, 2 only partially, and 2 not at all. The clients most likely to require a workaround for this feature are Outlook (New), Outlook Classic, Gmail Android. Each of them needs a tailored fallback. See the per-client examples above for the specific code fix Emailens recommends.

When in doubt, ship a baseline that renders without background-size and treat it as progressive enhancement on clients where support is verified. Emailens automatically detects cross-client divergence on this feature when you preview an email, so you can see exactly which template paths break before a campaign goes out.

Related Features

!important accent-color align-items animation aspect-ratio backdrop-filter background background-blend-mode

Check your own HTML for background-size

Paste your own, or run the sample below. Analyzed in this page, with no signup and nothing stored.

Zero-Friction Engine Preview

Test your background-size layout across 21 email clients

Preview rendering, catch CSS issues, and see how background-size displays across Outlook, Gmail, and Apple Mail. Free, no account needed.

Instant live preview · No signup required · 21 email engines

Last tested upstream: Feb 28, 2019 · Last synced by Emailens: Sep 2, 2026

caniemail.com (MIT) records Feb 28, 2019 as the last time background-size was tested in a real client, 7 years before this sync. Syncing copies that result forward, it does not re-test it. Carried in @emailens/engine data v0.12.2.