Gmail has very limited font support. Even if you specify a custom font using the <font> tag or CSS, Gmail will only render fonts that it natively supports. Any unsupported font will simply fall back to a default system font.
Below is the list of fonts that Gmail currently supports. These are standard system fonts, and Gmail does not support Google Fonts or any other web-hosted fonts.
Supported Fonts in Gmail
Arial
Arial Black
Arial Narrow
Bookman Old Style
Book Antiqua
Charcoal
Courier
Courier New
Comic Sans MS
Fixed Width (monospace)
Garamond
Geneva
Georgia
Helvetica
Impact
Lucida Console
Lucida Grande
Lucida Sans Unicode
Monaco
Monospace
MS Sans Serif
Narrow (Arial Narrow)
New York
Palatino
Palatino Linotype
Roboto
Sans Serif (Arial fallback)
Serif (Times New Roman fallback)
Symbol
Tahoma
Times
Times New Roman
Trebuchet MS
Verdana
Webdings
Wide (Arial Black)
Wingdings
Zapf Dingbats
Because of these restrictions, if your email design depends on a custom font, it’s recommended to provide a reliable fallback font from the list above to ensure consistent rendering across Gmail.