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Sending DKIM signed e-mail messages over SMTP in Rust

- 1 min read
Mauro D.
Mauro D.
Project Maintainer
  • 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", "[email protected]"))
            .to(vec![
                ("Jane Doe", "[email protected]"),
                ("James Smith", "[email protected]"),
            ])
            .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", "[email protected]"))
            .to("[email protected]")
            .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!

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