Machine has internet connection, but cannot ping or send email

I have a user with a machine that complains he cannot receive email. I remoted into his machine and found that he cannot ping either the incoming or outgoing mail server from his machine. In fact, it seems as if he cannot ping any websites. The few I tried all came back as requests timed out. The user is able to get online. I was not able to ping his machine from mine. The user went to a machine right next to his and was able to ping the incoming and outgoing mail servers without a problem.

I’ve flushed the DNS cache and rebuilt the TCP/IP stack. I’d appreciate any help with this matter. Thank you.