Mail: smtp proxy without authentication. Activated by auth method "unauth" in smtp_auth directive. Waits for MAIL FROM and first RCPT TO from client, asks auth_http for backend with additional headers Auth-SMTP-Helo, Auth-SMTP-From, Auth-SMTP-To, and establishes connection to backend. Auth-SMTP-From/To currently contain full command (e.g. "mail from: <>"), this may change in future. The functionality was designed to take off load from real smtp servers. Additionally it may be used to implement pop-before-smtp authentication (but dont do it unless you really need it - use real auth instead). Current bug-features: - If only "unauth" method activated in config, other methods (e.g. plain, login) not advertised but accepted. Make sure your auth server handles this gracefully. - If backend server returns error on MAIL FROM / RCPT TO command while proxy tunnel setup, nginx will close connection to client with 4xx error. One may use proxy_pass_error_message directive to pass original error message to client. - Syntax of MAIL FROM / RCPT TO commands from client isn't checked.