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A short description of the issue: On non-enterprise www gmail clients, background-url property is recently stripped from HTML of emails.


Send the following HTML content with text/html email headers:

```
<div style='height:400px;width:400px;background-image:url("https://i.imgur.com/SvumxSO.jpeg");'><p><a href="https://www.google.com/"></a> Sample Image</p></div>
```

What steps will reproduce the problem?
1. Image will render on Android Gmail app, but not web gmail client.

> What is the expected output?
We should see the image

> What do you see instead?
The CSS tags are omitted

Other email clients including gmail mobile properly renders an image.