To be able to change font of your email templates, you need to request HTML editor to be enabled for your account. Contact us in Live Chat or via email: [email protected].
When it's enabled, the source code icon will appear in the tool bar.
Here's the example how to wrap your text so the font will be applied:
<span style="font-size: 11px; font-family: georgia; color: black;"> your email body text here </span>