I had applied for an academic internship after my undergraduate studies. The professor has accepted me for the internship. But since then he has not properly replied to my emails. I need his letter for VISA purposes. How should I write an email to him asking for the same? I had sent an email to him regarding this but he has not replied to the email. The problem is that I can't write a proper email and also he is the director of the institute and is probably very busy.
Could you please help me with writing such an email. Also I am taking a year gap for this internship, so this is extremely important to me. I also want to convey him that this internship is extremely important to me.