Postmasters sometimes faces delicate ethical choices as the flow of e-mail comes across their screen. Pat McGregor wrote a paper for the ACM SIGUCCS conference, Fall 1989, called Averting One's Eyes -- Ethical approaches to Postmastering.
Encryption can help you achieve privacy. You can learn about PGP and other privacy matters by visiting The Privacy Pages and Netsurfer Focus on Cryptography and Privacy. Nathan Ensmenger has published a page for this class on Cryptography Resources.
The folks at the National Computer Security Association have many books for sale on the subject of Computer Privacy & Ethics.
Who are you? How do I know that you are really you? There are several ways to establish your identity in cyberspace.
Your digital signature is intended to act like your real signature. The Electronic Freedom Foundation (EFF) has a great collection in Privacy - Crypto - Digital Signature, ID & Authentication" Archive. The State of Washington hosts a site for digital signature Frequently Asked Questions. If you'd like to read the technical specifications published by the Federal Government, then check out FIPS PUB 186, the Digital Signature Standard (DSS).