Rust
Send HTML Email with External CSS as Related Item

Demonstrates how to compose an HTML email with an external CSS file included as a related item and referenced by CID (Content-ID).
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Rust

// 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.
let mailman = chilkat::MailMan::new();

// Use your SMTP server hostname.  This example uses office365, but it could be any SMTP server..
mailman.set_smtp_host("outlook.office365.com");
mailman.set_smtp_port(587);
mailman.set_start_tls(true);

// Set the SMTP login/password
mailman.set_smtp_username("OFFICE365-SMTP-LOGIN");
mailman.set_smtp_password("OFFICE365-SMTP-PASSWORD");

// Create a new email object
let email = chilkat::Email::new();
email.set_subject("HTML Email with embedded CSS");
email.set_from("Chilkat Support <my-office365-user@mydomain.com>");
let _ = email.add_to("Chilkat Support", "support@chilkatsoft.com");

let sb_css = chilkat::StringBuilder::new();
let b_crlf = true;
let _ = sb_css.append_line("body {", b_crlf);
let _ = sb_css.append_line("    background-color: powderblue;", b_crlf);
let _ = sb_css.append_line("}", b_crlf);
let _ = sb_css.append_line("h1 {", b_crlf);
let _ = sb_css.append_line("    color: blue;", b_crlf);
let _ = sb_css.append_line("}", b_crlf);
let _ = sb_css.append_line("p {", b_crlf);
let _ = sb_css.append_line("    color: red;", b_crlf);
let _ = sb_css.append_line("}", b_crlf);

// It's possible to add a CSS file directly by calling AddRelatedFile.
// This example will add the CSS from a string.
let filename_in_html = "styles.css".to_string();
let Ok(content_id_css) = email.add_related_string(&filename_in_html, &sb_css.get_as_string().unwrap_or_default(), "utf-8") else {
    println!("{}", email.last_error_text());
    return;
};

// The src attribute for the image tag is set to the contentIdCss:
let sb_html = chilkat::StringBuilder::new();
let _ = sb_html.append_line("<!DOCTYPE html>", b_crlf);
let _ = sb_html.append_line("<html>", b_crlf);
let _ = sb_html.append_line("<head>", b_crlf);
let _ = sb_html.append_line("  <link rel=\"stylesheet\" href=\"cid:CONTENT_ID_CSS\">", b_crlf);
let _ = sb_html.append_line("</head>", b_crlf);
let _ = sb_html.append_line("<body>", b_crlf);
let _ = sb_html.append_line("", b_crlf);
let _ = sb_html.append_line("<h1>This is a heading</h1>", b_crlf);
let _ = sb_html.append_line("<p>This is a paragraph.</p>", b_crlf);
let _ = sb_html.append_line("", b_crlf);
let _ = sb_html.append_line("</body>", b_crlf);
let _ = sb_html.append_line("</html>", b_crlf);

let num_replacements = sb_html.replace("CONTENT_ID_CSS", &content_id_css);

email.set_html_body(&sb_html.get_as_string().unwrap_or_default());

if mailman.send_email(&email).is_err() {
    println!("{}", mailman.last_error_text());
} else {
    println!("Mail Sent!");
}