We tested these email clients using internal test tools and email preview services.

Fully supported
All the options work properly. Fall-back elements show for image backgrounds and web fonts.

Desktop
Apple Mail 8, 9 & 10
Thunderbird
Airmail2
Microsoft Outlook for Mac 2011, 2016
Microsoft Outlook for Windows 2007, 2010, 2011, 2013, 2016 *

* Background images and web fonts are not supported

Mobile
Android 4.4 Mail
Gmail App (iOS)
Gmail App (Android)*
iOS Mail (iPhone & iPad)
Outlook App (Android & iOS)**
Samsung Mail App (Android)
Yahoo App (Android & iOS)

* When using a Gmail account

** Will show the desktop version when using Microsoft email accounts

Web
Gmail
G Suite
Inbox by Gmail
Outlook.com
Office 365
Yahoo
AOL Mail
Comcast
freenet.de
GMX.de
Mail.ru
Libero Mail
Tiscali
Virgilio
email.it
Web.de
Centrum.cz
Seznam.cz, Post.cz, Email.cz
Note: none of the above services supports web fonts

Partial support for some options
Messages display correctly, but some options (with low impact) may not display as expected.

Desktop
Windows 10 Mail *
Microsoft Outlook 2013 in high-resolution displays *
Microsoft Outlook 2016 in high-resolution displays **
Microsoft Outlook 2000, 2002 & 2003 ***

  • Background images and web fonts are not supported. Applies a font resize that may expand the layout.

** Background images and web fonts are not supported. Applies a font resize that may expand the layout. The text is scaled at 200% by default in some devices.
*** Web fonts are not supported. Buttons don't display round corners. Social icons are not flexible.

Web
qq.com *
Yandex.ru
* Buttons doesn't display properly.

Not yet supported
This list includes new and updated mobile email clients with compatibility issues.
Huawei Mail App (Android)

Only basic settings works
When sending to this clients, we recommend using text and images in a simple one-column layout.

Desktop
Lotus Notes 7, 8 & 8.5
IBM Notes 9

Mobile
Gmail App using IMAP accounts
Web clients (mobile versions)

Web
T-online.de

E-mail servers
Some email servers alter sent email code.

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