Rust

Get the Content-ID of an Attachment

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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Rust

// 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).

let email = chilkat::Email::new();
email.set_subject("Attachment Content-ID");

let _ = email.add_string_attachment("notes.txt", "Some notes.");

// Get the Content-ID of the first attachment (may be empty if none was assigned).
let cid = email.get_attachment_content_id(0).unwrap_or_default();
println!("Attachment 0 Content-ID: {}", cid);