Get the Content-ID of an Attachment

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Demonstrates the Chilkat Email.GetAttachmentContentID method, which returns the Content-ID header field for the Nth attachment. The index is zero-based, so the first attachment is 0. This example adds an attachment and reads its Content-ID (which may be empty when none was assigned).

Background: A Content-ID is a unique identifier for a MIME part. It is essential for inline "related" resources, where HTML references an image by cid:, but ordinary file attachments usually have none. Reading it is useful when inspecting how a message is assembled, or when distinguishing parts that are referenced from the body versus those meant purely as downloadable attachments.

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//  Demonstrates the GetAttachmentContentID method, which returns the Content-ID header
//  field for the Nth attachment.  The index is zero-based (the first attachment is 0).

Chilkat.Email email = new Chilkat.Email();
email.Subject = "Attachment Content-ID";

email.AddStringAttachment("notes.txt","Some notes.");

//  Get the Content-ID of the first attachment (may be empty if none was assigned).
string cid = email.GetAttachmentContentID(0);
Debug.WriteLine("Attachment 0 Content-ID: " + cid);