I am emailing a friend in Nairobi & every time he tries to reply they bounce back to him undelivered to me.?

Can anyone explain this and tell me if I can do anything to get the messages as I desperately need to recieve them?
I am emailing a friend in Nairobi %26amp; every time he tries to reply they bounce back to him undelivered to me.?
is he in your address book? sometimes your provider thinks it is spam if they aren't in your address book. try that!