如何使用MimeKit/MailKit设置内容传输编码？

var message = new MimeMessage();

var textPart = new TextPart("plain")
{
    Text = "This is the plain text content of the email."
};

var htmlPart = new TextPart("html")
{
    Text = "<p>This is the HTML content of the email.</p>"
};

textPart.ContentTransferEncoding = ContentEncoding.Base64;
htmlPart.ContentTransferEncoding = ContentEncoding.QuotedPrintable;

message.Body = new Multipart("alternative")
{
    textPart,
    htmlPart
};

message.From.Add(new MailboxAddress("Sender Name", "sender@example.com"));
message.To.Add(new MailboxAddress("Recipient Name", "recipient@example.com"));
message.Subject = "Email Subject";

using (var client = new SmtpClient())
{
    client.Connect("smtp.example.com", 587, false);
    client.Authenticate("username", "password");
    client.Send(message);
    client.Disconnect(true);
}