Mr. Hosseini is the best student I have taught in my 15 years of teaching. I am confident that he would be an outstanding addition to your program. I give him my highest recommendation. I would be pleased to answer any additional questions you may have. *I had to guess the context a little bit in the first sentence. It may not be accurate to what you are trying to say. As others indicated it is better without "To recapitulate," I personally would probably also remove "without doubt" because it doesn't add anything to the statement. I changed the the 3rd sentence slightly to sound more natural.

" is the best student FOR ...." In the title " appreciate".

It's pretty good, actually. But "recapitulate" is weird here. I would leave that out. Just start the sentence, "Without doubt..."

Yes, I meant that. Thank you

To summarise instead of recapitulate. "Is the best student in 15years" doesn't really make sense. Are you trying to say in the 15 years, he has been the best?