eM currently allows the user to specify the preferred font for reading, and then to include that font for fixed-width messages. This eliminates the possibility of specifying different fonts for fixed-width and proportional fonts. This feature would be useful, because I have a preferred font for each type, but they are not the same.
Because the fonts are not part of an e-mail, but have to be installed on the respective system, a “default setting” for different fonts is “chic” at best for the creation - on receipt, a (formatted) e-mail can express “wishes”, but these wishes are only fulfilled if the target system has the required fonts - which is by no means guaranteed.
Therefore, you can define your “text only font”. All formatted font commands, possibly pasted from a textprocessor, can look alike for the receiver, but they haven’t to. Maybe this is the reason for the limited settings: Avoiding an impression that cannot be fullfilled.
BUT: Have you tried the possibilities given by the templates? You may set your preferred font there, you can define as much templates as you like,…