Many users on this site use their real identity. So, via google or a linked website, it is usually easy to find the contact details of a fellow user. However, in cases when users wish -- for whatever reason -- to keep their identity secret, what is the protocol for private contact? (This is not a cryptography question, btw.)
This is somewhat related to the question on using actual names. Adding a private email function has its issues and one of these might be that it removes one less incentive for giving your true identity.
This question occurred to me while answering When should you say what you know?.