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 Apple Mail?

background-size works in Apple Mail. Closest to Thunderbird: Apple Mail, which agrees on 219 of the 261 features both are tested on.

background-size in Thunderbird

Works background-size works in Thunderbird.

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

The fix for the clients that need it

Needed in 4 of 21: Outlook Classic, Gmail Android, Gmail iOS and 1 more.

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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Your next question

Every feature in Thunderbird · 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.
Does background-size work in Apple Mail?: background-size works in Apple Mail. Closest to Thunderbird: Apple Mail, which agrees on 219 of the 261 features both are tested on.

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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