File list (Check if you may need any files):
socket_programming
..................\socket_programming
..................\..................\simple SMTP
..................\..................\...........\EmailSender.java
..................\..................\UDP Pinger
..................\..................\..........\client
..................\..................\..........\......\PingMessage.java
..................\..................\..........\......\UDPClient.java
..................\..................\..........\......\UDPPinger.java
..................\..................\..........\server
..................\..................\..........\......\UDPServer.java
..................\..................\带身份验证的SMTP
..................\..................\................\EmailSender2.java