Sending DKIM signed e-mail messages over SMTP in Rust

Building and sending e-mails securely does not have to be complicated. Today the mail-send crate was released including the following features:

• Generates e-mail messages conforming to the Internet Message Format standard (RFC 5322) with full MIME support (RFC 2045–2049) and automatic selection of the most optimal encoding for each message body part.
• DomainKeys Identified Mail (DKIM) Signatures (RFC 6376).
• SMTP support with TLS and multiple authentication mechanisms (XOAUTH2, CRAM-MD5, DIGEST-MD5, LOGIN and PLAIN).
• Full async (requires Tokio).

Composing and sending an e-mail message via SMTP is as simple as:

    // Build a simple multipart message
    let message = MessageBuilder::new()
        .from(("John Doe", "john@example.com"))
        .to(vec![
            ("Jane Doe", "jane@example.com"),
            ("James Smith", "james@test.com"),
        ])
        .subject("Hi!")
        .html_body("<h1>Hello, world!</h1>")
        .text_body("Hello world!");

    // Connect to an SMTP relay server over TLS and
    // authenticate using the provided credentials.
    Transport::new("smtp.gmail.com")
        .credentials("john", "p4ssw0rd")
        .connect_tls()
        .await
        .unwrap()
        .send(message)
        .await
        .unwrap();

And to sign a message with DKIM just do:

// Build a simple text message with a single attachment
    let message = MessageBuilder::new()
        .from(("John Doe", "john@example.com"))
        .to("jane@example.com")
        .subject("Howdy!")
        .text_body("These pretzels are making me thirsty.")
        .binary_attachment("image/png", "pretzels.png", [1, 2, 3, 4].as_ref());

    // Set up DKIM signer
    let dkim = DKIM::from_pkcs1_pem_file("./cert.pem")
        .unwrap()
        .domain("example.com")
        .selector("2022")
        .headers(["From", "To", "Subject"]) // Headers to sign
        .expiration(60 * 60 * 7); // Number of seconds before this signature expires (optional)

    // Connect to an SMTP relay server over TLS.
    // Signs each message with the configured DKIM signer.
    Transport::new("smtp.example.com")
        .dkim(dkim)
        .connect_tls()
        .await
        .unwrap()
        .send(message)
        .await
        .unwrap();

More examples can be found on Github. Enjoy DKIM signing!