Or perhaps you've just read a great email on one of the discussion lists you're on. The problem is, the author didn't use a sig file and the return address is obviously a nickname. Sleuthing on the Net Despair not. There's more than one way to find a person. Figure out what information you do have and use an appropriate reverse lookup.
Reverse lookups are just what they imply.
They're databases full of contact information. Instead of searching by name however, you can search via email address, fax number, phone number or employer. Let's say you have a phone number but no name. Simply choose the appropriate reverse lookup, type in the number and if all goes well, you'll find the name and address of the person it belongs to. Or maybe you have an email address but nothing else.