I’m trying to set Aptos (Microsoft’s new standard font) as a specific font option when composing emails in Mailspring.
I have already tried creating a custom theme by modifying the .less files (specifically ui-variables.less and composer.less). While I can visually force the font via CSS using font-family: 'Aptos' !important;, I am facing two main issues:
Aptos does not appear in the font dropdown menu within the Composer toolbar.
I want to ensure the font is correctly applied to the outgoing email’s HTML so that recipients (who have the font installed) can see it properly.
I have access to the source code and noticed that the Composer pulls components from mailspring-component-kit. Does anyone know which file contains the toolbar font definitions (the FONT_FAMILIES array) or if there is a cleaner way to register a new font without having to recompile the entire app?
The font picker list is hardcoded in app/src/components/composer-editor/base-mark-plugins.tsx in the DEFAULT_FONT_FACE_OPTIONS array — there’s no plugin API to add entries to it without modifying that file and rebuilding. That said, there’s a workaround: you can type any CSS font-family value directly into the font picker’s text field if your theme exposes it as an editable input, or you can select some text and paste <font style="font-family: Aptos"> in the raw HTML view.
The bigger issue is that Aptos is a Microsoft-bundled font, so recipients on macOS or Linux won’t have it installed and their clients will fall back to a system font. For composed HTML email, web-safe fonts (or fonts with wide OS coverage like Arial, Georgia, or Verdana) are much more reliable. I’ll note the font list extensibility as a feature request — it’s a reasonable ask.
Yes, I am well aware that the Aptos font is specific to Microsoft. However, since I heavily use Mailspring as my client for business email—which relies heavily on Exchange—I really needed to use that specific font.
I’m sure making the modification and then recompiling everything is no easy task. I will look into it properly and then proceed with the tweak if necessary.
By the way, are there any plans for a native Mac version?