How to set content transfer encoding for MVC mail message?

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C#

MVC5

mail

While receiving this mail in Gmail I am getting content transfer encoding as quoted-printable which results displaying mail in unreadable format for the user (base64 content without encoding), So How can I change Email content transfer encoding header value as base64

What I have tried:

var client = new System.Net.Mail.SmtpClient(ServerName, ServerPort);

MvcMailMessage mailMessage = new MvcMailMessage { Subject = "Subject" };
mailMessage.IsBodyHtml = true;
mailMessage.BodyEncoding = System.Text.Encoding.UTF8;
mailMessage.BodyTransferEncoding = System.Net.Mime.TransferEncoding.Base64;
message.From = "test@gmail.com"
message.Headers.Add("Content-Transfer-Encoding", "base64");
mailMessage.Attachments.Add(new Attachment(stream, "testfile"));

PopulateBody(mailMessage, viewName: "Emailview", linkedResources: resources);

client.Send(message);