Has your son checked his e-mail folders including the junk and deleted folders? Is it possible that the message are being filtered due to a user created rule? Is there anything that could be considered spammy in the e-mail that you are sending that would cause Hotmail to block it, yet your local ISP to also block and not return the bounce message to you? Is it possible that you local ISP is on a blacklist and Hotmail is currently deferring or rejecting email from them? If you send a test email to email@example.com I can let you know if your ISP is blacklisted. That would make sense if the same e-mail sends OK to Hotmail from Gmail but not from your local ISP.