In general, a small subset of system fonts (such as Arial, Helvetica, Times New Roman, Trebuchet, Courier, etc.), are the only safe fonts to use for HTML email, and should be implemented as fallback fonts in the event that your intended recipient does not have universal font support within their email client. Plus, many HTML attributes and CSS properties are only inconsistently implemented and supported.
Coding HTML requires a keen eye and attention to detail. It only takes one mistake (missing tag, unsupported font, etc.) to destroy the intended result!