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CSS property · data last changed 10 Nov 2026

background-size in email clients

Works in 17 of 21. Not supported in Outlook Classic. Partial in Gmail Android, Gmail iOS and Yahoo Mail.

Your reader in Outlook Classic sees the email without background-size, even if it looks right where you tested it.

caniemail (MIT) via @emailens/engine 0.18.22

What to do instead in Outlook Classic

Outlook ignores background-size; use VML or sized images

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

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background-size is not among the 24 features we have screenshotted on real installs. The ones we have →

All 21 clients, problems first

ClientSupport
Outlook Classic Not supported See caveat 2
Gmail Android Partial See caveat 1
Gmail iOS Partial See caveat 1
Yahoo Mail Partial See caveat 3
Works in 17: Gmail, Outlook 365, Outlook (New) and 14 more. Show all
ClientSupport
Gmail Works
Outlook 365 Works
Outlook (New) Works
Outlook iOS Works
Outlook Android Works
Outlook for Mac Works
Apple Mail Works
Apple Mail iOS Works
Yahoo Mail Android Works See caveat 4
Yahoo Mail iOS Works See caveat 4
Samsung Mail Works
Thunderbird Works
HEY Mail Works
Proton Mail Works
AOL Mail Works See caveat 4
Fastmail Works
Superhuman Works

Caveats (4)

  1. 1. Gmail Android, Gmail iOS: Partial. Not supported with non Google accounts. But it can be used in the background shorthand property instead.
  2. 2. Outlook Classic: Background images size can be used in VML with the size attribute. See VML documentation.
  3. 3. Yahoo Mail: Observed 2026-11-09 (Emailens real-device checks, Yahoo Mail web (Chrome): foodpanda campaign (2026-10-28), AliExpress (2026-11-09)): Partial. Ignored inside the background shorthand (background: url() 0 0 / cover): the image draws at its natural size. The background-size property written on its own works.
  4. 4. Yahoo Mail Android, Yahoo Mail iOS, AOL Mail: Partial. Does not support multiple values. The comma between two values is removed.

Caveats as recorded by caniemail (MIT), one entry per wording.

Your next question

background-size in Outlook Classic · Every feature in Outlook Classic · All email CSS features · What real installs show

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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