Schedule Reminder Emails Formatting

Hello Andy,
I previously included a small amount of HTML in one of my emails advising those on the rota that it was their turn. Today I tried to improve the message and all the HTML disappeared. I tried to revert to the previous version, but none of the HTML would stick. My emails now look worse than before, with no carriage returns between lines!

Please can the HTML capability be restored?

Thank you,
Mark