(.NET Core C#) Add Header Field to MIME Sub-Header in Email

Demonstrates how to add a header field to one of the attachment sub-headers in an email.

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

Chilkat.Email email = new Chilkat.Email();

email.Subject = "test";
email.AddTo("Chilkat","support@chilkatsoft.com");
email.From = "Matt <matt@example.com>";
email.Body = "This is a simple plain-text body.";

bool success = email.AddFileAttachment2("qa_data/1.HPM","application/x-hprimnet");
if (success != true) {
    Debug.WriteLine(email.LastErrorText);
    return;
}

// Add a "ContentDescription: HPM/3.0" in the attachment's sub-header.
// The 1st attachment is at index 0.
email.AddAttachmentHeader(0,"Content-Description","HPM/3.0");

// Show the email MIME:
Debug.WriteLine(email.GetMime());

// This is the output:
// (Note: When Chilkat sends email, all CKX-* headers are removed prior to sending.)

// MIME-Version: 1.0
// Date: Wed, 16 Jan 2019 10:05:18 -0600
// Message-ID: <93B88835586270B7BE5202F84E171F29C10BA935@CHILKATSLICE>
// Content-Type: multipart/mixed; boundary="------------000502000000020502010608"
// X-Priority: 3 (Normal)
// Subject: test
// To: Chilkat <support@chilkatsoft.com>
// From: Matt <matt@example.com>
// CKX-Bounce-Address: matt@example.com
// 
// --------------000502000000020502010608
// Content-Type: text/plain; charset=us-ascii; format=flowed
// Content-Transfer-Encoding: 7bit
// 
// This is a simple plain-text body.
// --------------000502000000020502010608
// Content-Type: application/x-hprimnet; name="1.HPM"
// Content-Transfer-Encoding: base64
// Content-Disposition: attachment; filename="1.HPM"
// Content-Description: HPM/3.0
// 
// FILE_DATA_IS_HERE...
// 
// --------------000502000000020502010608--