Gmail mobile webmail not supporting max-width:100%

[M-J-Robbins]

Email Client
Gmail webmail
Chrome 139

Operating System
Android 16
Pixel 8

Expected Result
When sending an <img> with max-width:100%, that image should retain max-width:100% and scale down to fit the mobile browser.

Actual Result
max-width:100% is replaced by max-width:1140px so the image doesn't scale down.

Steps to reproduce

• Send an email with the below code
• Open in Gmail on a mobile browser
• Select the image and copy
• Paste into https://customer.io/tools/what-does-it-paste to see the rendered code.

Code sample

<img src="https://email-placeholders.com/300x200" alt="" width="600" style="vertical-align: middle; max-width: 100%; " />

Additional context
I've only tested on my Android, I'll try and add more results when I can.

[M-J-Robbins]

Using width:100% works as expected.

[M-J-Robbins]

Just tested on iOS 18.6.2 and not seeing the issue.
Tested on my Samsung and I am seeing the issue.

So looks like this is only on Android

[zalexstudios]

Don't use max-width: 100%; use - max-width: 600px