Email-safe fonts
Typefaces that render in mail clients without being downloaded.
Web fonts are unreliable in email: several major clients ignore font files altogether and fall back to a default. Email-safe fonts are the ones already installed nearly everywhere — Arial, Georgia, Verdana, Times New Roman and a handful more.
You can still specify a brand font, as long as the font stack behind it degrades to something you have looked at. The failure mode is not “no font”, it is “a font you never chose”, and a fallback with different proportions will change your line breaks.
Where the brand face genuinely matters — a logo, a short headline — an image is more predictable than a font, provided it has alt text.