Hotmail will not receive messages from Gmail

For about six months now, my friend's hotmail account has not been able to receive e-mails send from my Gmail account. I do not receive any notification failures from Gmail, and my friend does not have me on a blocked list. I can send and receive e-mails to/from him from other accounts, and he receives e-mails from other Gmail users. I have been through the diagnostic on Gmail's website, which suggests the problem is with hotmail. Is there a solution to this problem other than creating a new account?