在C＃中使用.NET MailMessage发送加密和签名的邮件

Question

我想发送加密并签名的邮件，而不使用任何第三方库。 我可以发送经过签名或加密的电子邮件。但是两者都不起作用。 我尝试用Thunderbird发送邮件，并查看了源，但是没有任何内容表明邮件已加密并签名。 当我使用以下代码时

byte[] bodyBytes = Encoding.UTF8.GetBytes("TestBody");
SignedCms cms = new SignedCms(new ContentInfo(bodyBytes), false);
CmsSigner signer = new CmsSigner(SubjectIdentifierType.IssuerAndSerialNumber, signerCert); //X509Certificate2 with private key of sender
cms.ComputeSignature(signer);
byte[] signedBytes = cms.Encode();
EnvelopedCms ecms = new EnvelopedCms(new ContentInfo(signedBytes));
CmsRecipient cmsr = new CmsRecipient(SubjectIdentifierType.IssuerAndSerialNumber, encryptCert); //X509Certificate2 with public key of recipient
ecms.Encrypt(cmsr);
byte[] encryptedBytes = ecms.Encode();
MailMessage msg = new MailMessage();
msg.To.Add(new MailAddress(to));
msg.From = new MailAddress(from);
msg.Subject = subject;
MemoryStream ms = new MemoryStream(encryptedBytes);
AlternateView av = new AlternateView(ms, "application/pkcs7-mime; smime-type=enveloped-data;name=smime.p7m");
msg.AlternateViews.Add(av);
SmtpClient smtp = new SmtpClient("[smtpServer]", 25);
smtp.Send(msg);

MailClient只是解密或检查邮件的签名..我最后执行的操作。如何告诉客户端同时执行解密和签名检查？