This site uses personal contact forms, where members can send one another an e-mail. (This is only available to logged-in members.) Also, through site-wide contact forms, members or non-members can send e-mails to the site maintainers.
With either form, members can specify a subject, write their message, and also have a copy of their e-mail sent to their own address. Through contact forms, members allow themselves to be contacted yet keep their own e-mail addresses private until the message is replied to.
As a member, you can also enable or disable your personal contact form. When the form is enabled, a contact tab is displayed in your user profile, for everyone to see. When you visit your own profile, the contact tab is not displayed. However, it is displayed to other users.