System.Net.Mail - 尝试发送带有附件的邮件到gmail,但仅适用于小附件

using System.Net.Mail;

// 创建一个邮件对象
MailMessage mail = new MailMessage();

// 设置邮件的发件人、收件人和邮件主题
mail.From = new MailAddress("from@example.com");
mail.To.Add("to@example.com");
mail.Subject = "Test Email with Attachment";

// 添加邮件的正文内容
mail.Body = "This is a test email sent from .NET Framework with an attachment.";

// 添加附件
mail.Attachments.Add(new Attachment("C:\\path\\to\\attachment.txt"));

// 发送邮件
SmtpClient smtp = new SmtpClient("smtp.gmail.com");
smtp.Port = 587;
smtp.Credentials = new NetworkCredential("username", "password");
smtp.EnableSsl = true;
smtp.Send(mail);