用MailKit和Stringbuilder发送ics文件

using MailKit.Net.Smtp;
using MimeKit;
using System.Text;

StringBuilder stringBuilder = new StringBuilder();
stringBuilder.AppendLine("BEGIN:VCALENDAR");
stringBuilder.AppendLine("VERSION:2.0");
// 添加ics文件的其他内容
stringBuilder.AppendLine("END:VCALENDAR");

MimeMessage message = new MimeMessage();
message.From.Add(new MailboxAddress("发件人姓名", "发件人邮箱"));
message.To.Add(new MailboxAddress("收件人姓名", "收件人邮箱"));
message.Subject = "ICS文件";

MimePart attachment = new MimePart("text/calendar")
{
    Content = new TextPart("calendar")
    {
        Text = stringBuilder.ToString()
    },
    ContentDisposition = new ContentDisposition(ContentDisposition.Attachment),
    ContentTransferEncoding = ContentEncoding.Base64,
    FileName = "calendar.ics"
};

message.Body = new Multipart("mixed")
{
    attachment
};

using (var client = new SmtpClient())
{
    client.Connect("SMTP服务器地址", 端口号, false);
    // 如果需要身份验证，可以在此处设置用户名和密码
    // client.Authenticate("用户名", "密码");
    client.Send(message);
    client.Disconnect(true);
}