Maybe you can use a an eM Client “Mail Template” to put in a fallback font for the receiver as @Victor.David suggested in his post in the following thread.
Fonts need to exist on the device that receives / reads the email, or the email client needs to insert a web accessible reference to the desired font. It can do this via import statements or other syntax:
@import url`('https://fonts.googleapis.com/css?family=Open+Sans');
@import url`('https://fonts.googleapis.com/css?family=Calibri');
<link href="https://fonts.googleapis.com/css?family=Open+Sans" rel="stylesheet">
... more
If the receiver doesn’t have the font on the device and no external ref…