用C#写一个动态发送邮件的小程序，实现基本的邮件发送，修饰功能不多，输入发件人、收件人、邮件主题、邮件正文即可发送邮件。-Using C# to write a small program to send mail dynamically, to achieve the basic message is sent, modified function of small, enter the sender, recipient, subject line, message body to send