settings for larger text won’t stay for emails

I have my settings for emails  the 16 size and for Comic Sans but every time I type an email the size goes right back to 12 .  The font I set does work some times.  Also, while typing a message and go back to the beginning  of the sentence to correct a word or add a comma the size and fonts go right back to the default.  How many time do I have to fix the settings for them to stay put!!