...it's not unusual for Outlook to revert to default fonts, etc. In order to save my favorite messages settings, I open a new message, create the new settings, but then leave the message blank, then save a copy to the "Documents" folder or my desktop. (Click on "File" in the upper left, choose "Save As", then name the file something like Template, etc. and save it to the location of your choice.)

From that point on, when I'm going to send a new message, I simply open the blank "Template" file on the desktop, create the new message and send it.. The blank template with your saved settings will remain for further use whenever you need it.

Hope this helps.