Rust

Add a Custom Header Field to an Email

Demonstrates the Chilkat Email.AddHeaderField method, which adds a standard or custom header field. If the field already exists, this method replaces it (use AddHeaderField2 to allow duplicates). Header fields whose names begin with CKX- are not transmitted when the email is sent, but are preserved across XML save/load, making them handy for persistent metadata. This example adds a custom X- header and reads it back.

Background: Beyond the well-known headers (From, Subject, etc.), MIME lets you add arbitrary fields. By convention custom, non-standard fields are prefixed with X-, so mail systems know not to expect them in the standards. Applications use these to carry tracking IDs, campaign tags, or routing hints. Chilkat's CKX- convention goes a step further — those fields live with the object but are stripped before the message is actually sent.

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Rust

// Demonstrates the AddHeaderField method, which adds a standard or custom header field.
// If the header field already exists, this method REPLACES it.  (To allow duplicates,
// use AddHeaderField2 instead.)  Header fields whose names begin with "CKX-" are not
// transmitted when the email is sent, but are preserved when saved to/loaded from XML.

let email = chilkat::Email::new();
email.set_subject("Custom header example");
email.set_from("alice@example.com");

// Add a custom header field.
email.add_header_field("X-Custom-Header", "custom value");

println!("X-Custom-Header = {}", email.get_header_field("X-Custom-Header").unwrap_or_default());