Hobo, before you drop yourself in it, Goggle "who is" without the quotes. I believe you can also ping an IP address and find out if the PC is in use. In the old days ISPs never revealed an IP address owner unless the Police were involved. However the rules have changed and if the recipient feels harrassed or threatened by your e-mail I believe you have a right to the details of the sender within seven days. There are a number of IP address search methods available on the net. You could start with RIPE.org which is the EU registry of all EU IP addresses, it also gives you all the other Registers used abroad. Confidential e-mail?