(.NET Core C#) Send Signed Email using PFX File (long version)

Demonstrates how to send a signed email using a digital certificate w/ private key stored in a PFX file.

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// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

// The mailman object is used for sending and receiving email.
Chilkat.MailMan mailman = new Chilkat.MailMan();

// Set the SMTP server.
mailman.SmtpHost = "smtp.mymailserver.com";

// Create a new email object
Chilkat.Email email = new Chilkat.Email();

email.Subject = "This email is signed";
email.Body = "This is a digitally signed mail";
email.From = "Chilkat Admin <admin@chilkatsoft.com>";
bool success = email.AddTo("Chilkat Support","support@chilkatsoft.com");

// Indicate that the email should be sent signed.
email.SendSigned = true;

// Load a PFX file into a certificate store object.
// Then locate the certificate matching the  sender's email address,
// and use it for signing.
// (a PFX file may contain more than one certificate.)
Chilkat.CertStore certStore = new Chilkat.CertStore();
// The 1st argument is the path of the PFX file, the 2nd arg is the 
// PFX file's password:
success = certStore.LoadPfxFile("/pfx_files/chilkatsoft_secret.pfx","secret");
if (success != true) {
    Debug.WriteLine(certStore.LastErrorText);
    return;
}

Chilkat.Cert cert = certStore.FindCertBySubjectE("admin@chilkatsoft.com");
if (certStore.LastMethodSuccess == false) {
    Debug.WriteLine(certStore.LastErrorText);
    return;
}

// Alternatively, if a PFX file is known to contain a single certificate,
// you may load it directly into a Chilkat certificate object.
// This snippet of source code shows how:
Chilkat.Cert cert2 = new Chilkat.Cert();
// The 1st argument is the filename, the 2nd arg is the 
// PFX file's password:
success = cert2.LoadPfxFile("/pfx_files/chilkatsoft_secret.pfx","secret");
if (success != true) {
    Debug.WriteLine(cert2.LastErrorText);

    return;
}

// This example will use the cert from the certStore...
success = email.SetSigningCert(cert);

// Signed email can be sent in two different ways.  
// In a multipart/signed email, the signature is attached as a separate MIME part.
// In an opaque email (signedData) the content of the email is encapsulated within the signature
// and the email is sent as "application/pkcs7-mime". 
// Either should be fine, but some receiving systems might require one or the other..
mailman.OpaqueSigning = false;

// Send a signed email.
success = mailman.SendEmail(email);
if (success != true) {
    Debug.WriteLine(mailman.LastErrorText);
}
else {
    // The LastErrorText property provides information
    // even when successful.
    Debug.WriteLine(mailman.LastErrorText);
    Debug.WriteLine("Mail Sent!");
}