As noted in the Meta.SE question JNat linked to, and in the related Meta.SE question, How do I contact other users?, the only out-of-band / user-to-user contact facilitated by Stack Exchange is if a user explicitly adds contact information to their profile (i.e., personal website where they might provide a contact link, Twitter handle, Github account name, etc).
In essence, Stack Exchange's outside contact policy is strictly opt-in for users to allow themselves to be contacted, and entirely under that user's control to determine the means of contact, by publicizing whatever information about themselves they wish.