Readdle, the team behind the Spark Mail app, says the latest update adds the ability to select your own choice of a font when drafting a new email or response.
You cam pick any one from Readdle’s new collection of fonts available in Spark for macOS and iOS devices. There’s a list of fonts and precise font-sizes to choose from for your messages.
Spark is free (https://sparkmailapp.com/pricing) to get started. For more features, you can upgrade to the Premium or Enterprise versions.