There is no way to do this. Unfortunately, email clients are too limited. Most of them cannot handle CSS3, not @ font-face (which uses font for icons). If you need Outlook support - you certainly want to - you shouldn't use icons as background images, either.
The only safe way is to convert each icon into images. Fortunately, iconmoon can help. Select the icons you need, choose to download as SVG / PNG, and use PNG files.
One more warning : use tables for the layout, for example, you were in 1998, without floats or fancy things.
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