Change font (impossible to read) when answer to a mail

Hello, 

I've got this problem : when I answer to a mail, the font change in a bad way , like this : 

"Cette brochure décrit en détail plus de 70 accidents observés sur la culture du maïs.
Des accidents liés aux carences, aux maladies, aux ravageurs, au climat, … "

Is anyone had ever seen this ? 

Thanks