说明：  根据SMTP协议写出的java小程序，实现邮件发送功能。适合初学计算机的学生。根据SMTP协议的要求直接处理协议的细节发送邮件，虽然比较麻烦了一些，但是对了解邮件协议的细节很有帮助的。
(According to the SMTP protocol written java applets, implement email functions. Suitable for novice computer student. According to the requirements of the SMTP protocol to deal directly with details of the agreement to send mail, although relatively trouble some, but the understanding of the message protocol details helpful.)