untrue unread email

Recently my email box show that I have 96 unread emails but when I open my email box which only show several unread emails . It continuously repeat again to show many unread emails after reading the box several hours . Yestday, two friends told me that they have sent an email to me but I have not received . Their record showed the email had sent to me. I found that I cannot receive some email. What is the problem ?