Description
You can use it if you want to make some content show on only mobile, not desktop when you make email templates.
The mobile content is hidden on a desktop but is shown on mobile.
The desktop content is shown on mobile but is hidden on a desktop.

It was test on Litmus(Apple Mail 10(os x 10.12), Apple Mail 11 (OS X10.13), Apple Mail 9 (OS X 10.11), Outlook 2007(Win7), Outlook 2010(Win7), Outlook 2011(OS X 10.10), Outlook 2013(Win7), Outlook 2013 120 DPI(Win7), Outlook 2016(OS X1.10), Outlook 2016(Windows7), Windows 10 Mail(Win10),Android 5.1, Android 6.0, Gmail App(Android 6.0), Gamil App(iOS 10.3.2), Gmail App IMAP(Android(android 4.4), Google Inbox(Android 6.0), Inboxby Gmail(iOS 10.3.2), iPhone6~8 plus, Outlook(Andorid 6.0), Samsung Mail(Android 6.0), AOL Mails, G Suite, Gmail(Chrome, Explorer, Firefox), Inbox by Gmail(Chrome), Inbox by Gmail(Firefox), Office 365 (Chrome, Explorer, Firefox), Outlook.com(Chrome, Explorer, Firefox), Yahoo! Mail(Chrome, Firfox))