E-mail paragraphs are cut short

I am working overseas and am using Yahoo as my browser. I have been sending out newsletters and a number (not all) have replied that the "paragraphs are cut short" For example, when the paragraph reaches a certain size, the paragraph ends (sometimes right in the middle of a word) and starts with the next paragraph on a new line. It seems to be if the paragraph is over about 780 characters is where it stops. If it was only one person, I would think it was their problem. If it was everyone, I would think it was my problem. Yahoo says it isn't their problem...
HELP! does anyone know what's happening?
Ed
epco2@yahoo.com