从memoryStream发送带有附件的MailKit电子邮件

var message = new MimeMessage();
message.From.Add(new MailboxAddress("发件人名称", "发件人邮箱"));
message.To.Add(new MailboxAddress("收件人名称", "收件人邮箱"));
message.Subject = "邮件主题";

// 设置邮件正文内容
var bodyBuilder = new BodyBuilder();
bodyBuilder.TextBody = "邮件正文";
message.Body = bodyBuilder.ToMessageBody();

var multipart = new Multipart("mixed");
multipart.Add(message.Body);

// 读取附件的数据到MemoryStream
var attachmentData = new byte[] { /* 附件的数据 */ };
var attachmentStream = new MemoryStream(attachmentData);

// 创建附件并添加到Multipart中
var attachment = new MimePart("application", "octet-stream")
{
    Content = new MimeContent(attachmentStream),
    ContentDisposition = new ContentDisposition(ContentDisposition.Attachment),
    ContentTransferEncoding = ContentEncoding.Base64,
    FileName = "附件文件名"
};
multipart.Add(attachment);

message.Body = multipart;

using (var client = new SmtpClient())
{
    client.Connect("SMTP服务器地址", 587, false);
    client.Authenticate("发件人邮箱", "发件人密码");
    client.Send(message);
    client.Disconnect(true);
}