That's a network address that your computer is trying to contact but it did not respond in a timely manner. The other computer may have been busy or you temporarily lost your network connection.
odd ... it's a 10. address ... this is a private address ... are you using your company's e-mail?
gobbl;e is right of course ... just if you are using your private mail ... not the type of address youd expect
It's because it's a private IP address that the mail has been rejected. Most routers will discard 10.x.x.x addresses meaning that it's impossible for the outside world to connect using this address.
You would normally have to go through a NAT (network address translator) to communicate with this network - perhaps there wasn't one, or there was a fault or something.