[tzimtzim]

i have recently had an arguement with a teacher because of a formal letter. i learned to write a formal letter without those lines in between the paragraphs. when i brought my letter to school, the teacher said it was going to get a bad mark because of that. however, i showed her an example of formal letter in cpe book, which didn't have lines in between the paragraphs and the teacher told me the book wasn't good...
then...is it true that writing a letter without lines in between the paragraf is incorrect? and if you do so...u get penalized in an exam?? or are there also other forms of writing formal letter accepted?