对象refrence不设置到对象的实例

当我试图发送一封电子邮件，在我的代码，它给了我一个错误，说

对象refrence不设置到对象的实例

可以请你帮忙吗？我不知道现在做什么。
- 新增 -

                  'send email

                  Try

                        Dim objemail As New _email()

                        objemail.from = System.Configuration.ConfigurationManager.AppSettings("UserName").ToString()

                        objemail.[to] = Convert.ToString(txt_email.Text)

                        objemail.subject = txtSubjects.Text

                        objemail.body = txt_Message.Text

                        objemail.IsHTML = False

                        objemail.SendMail()

                        lblSucc_Email.Text = "Email sent"

                  Catch er As Exception

                        lbl_error_Email.Text = er.Message

                  End Try