为什么在发送SMTP电子邮件时出现“无法分配属性”的信息？

mail.To

mail.From

using System.Net.Mail;...MailMessage mail = new MailMessage("you@yourcompany.com", "user@hotmail.com");SmtpClient client = new SmtpClient();client.Port = 25;client.DeliveryMethod = SmtpDeliveryMethod.Network;client.UseDefaultCredentials = false;client.Host = "smtp.gmail.com";mail.Subject = "this is a test email.";mail.Body = "this is my test email body";client.Send(mail);