I'm using the @font-face method to use the Open Sans family in an email newsletter. Is this the best way to do it? Or is the @import method better supported?

When I look at the email in my browser, I see Open Sans (I have Open Sans on my computer, but I have it disabled in Font Book). When I test through Litmus, both by sending through my ESP as well as copying and pasting HTML, the previews show the fallback font (Tahoma). Is this because I've added the font incorrectly in the CSS? Here's a portion of the email (without any client info/content):