The Message font and size preferences are used when creating a new template, and when switching a plaint text message to rich text.

To start a different font or size for a new template, set the message font and size in Fonts Preferences, then in the Templates Editor, click the plus button.

To change the font used when a plain text message is changed to rich text, set the message font and size in Fonts Preferences.

Plain text font shows the settings for displaying plain text email, which carries no font information or other formatting with it. This setting controls how you see plain text, but not how recipients see it.

To set the font and size used to display plain text messages, click the Change button and choose the font and size in the Fonts window.

Note: If you bring another Enclose window to the front after clicking Change, changing selections in the fonts window may not work. To get it to work again, click the Preferences window.

To have new messages created with rich text, check Start new messages in rich text (HTML).

Rich text is recommended for most uses. Plain text results in smaller messages, but some email programs used by your recipients may split the download link into multiple lines, causing it to produce an error when clicked. Rich Text (HTML) intrinsically avoids this problem.

However, on many group email lists (”listservs”), users are expected to send in plain text. You can switch any message to plain text by choosing Format > Make Plain Text.
Fonts Preferences