How many email clients support background-size?

It works in 17 of 21, partial in 3, not supported in Outlook Classic.

Does background-size work in Yahoo Mail iOS?

background-size works in Yahoo Mail iOS. Closest to Yahoo Mail: Yahoo Mail iOS, which agrees on 282 of the 298 features both are tested on.

background-size in Yahoo Mail

Partial background-size is partly supported in Yahoo Mail.

Observed 2026-11-09 (Emailens real-device checks, Yahoo Mail web (Chrome): foodpanda campaign (2026-10-28), AliExpress (2026-11-09)): Partial.

Works in 17 of 21 · partial in 3 · not supported in 1

Which clients

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

Your reader in Yahoo Mail may not see background-size the way you wrote it, even if it looks right where you tested it.

What to do instead in Yahoo Mail

Outlook ignores background-size; use VML or sized images

instead

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>

Show the original

before

3 lines

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

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What Yahoo Mail does with background-size

caniemail record, tested upstream 28 Feb 2019

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.

Your next question

Every feature in Yahoo Mail · background-size in every client

Questions

How many email clients support background-size?: It works in 17 of 21, partial in 3, not supported in Outlook Classic.
What do I use instead of background-size in Yahoo Mail?: Outlook ignores background-size; use VML or sized images.
Does background-size work in Yahoo Mail iOS?: background-size works in Yahoo Mail iOS. Closest to Yahoo Mail: Yahoo Mail iOS, which agrees on 282 of the 298 features both are tested on.

To see what else in your email Yahoo Mail does not support, paste the whole email.

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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