mail-auth

mail-auth is an e-mail authentication and reporting library written in Rust that supports the DKIM, ARC, SPF and DMARC protocols. The library aims to be fast, safe and correct while supporting all major message authentication and reporting RFCs.

Features:

• DomainKeys Identified Mail (DKIM):
  • ED25519-SHA256 (Edwards-Curve Digital Signature Algorithm), RSA-SHA256 and RSA-SHA1 signing and verification.
  • DKIM Authorized Third-Party Signatures.
  • DKIM failure reporting using the Abuse Reporting Format.
  • Key-pair generation for both RSA and Ed25519 (enabled by the generate feature).
• Authenticated Received Chain (ARC):
  • ED25519-SHA256 (Edwards-Curve Digital Signature Algorithm), RSA-SHA256 and RSA-SHA1 chain verification.
  • ARC sealing.
• Sender Policy Framework (SPF):
  • Policy evaluation.
  • SPF failure reporting using the Abuse Reporting Format.
• Domain-based Message Authentication, Reporting, and Conformance (DMARC):
  • Policy evaluation.
  • DMARC aggregate report parsing and generation.
• Abuse Reporting Format (ARF):
  • Abuse and Authentication failure reporting.
  • Feedback report parsing and generation.
• SMTP TLS Reporting:
  • Report parsing and generation.

Usage examples

DKIM Signature Verification

    // Create a resolver using Cloudflare DNS
    let resolver = Resolver::new_cloudflare_tls().unwrap();

    // Parse message
    let authenticated_message = AuthenticatedMessage::parse(RFC5322_MESSAGE.as_bytes()).unwrap();

    // Validate signature
    let result = resolver.verify_dkim(&authenticated_message).await;

    // Make sure all signatures passed verification
    assert!(result.iter().all(|s| s.result() == &DkimResult::Pass));

DKIM Signing

    // Sign an e-mail message using RSA-SHA256
    let pk_rsa =  RsaKey::<Sha256>::from_pkcs1_pem(RSA_PRIVATE_KEY).unwrap();
    let signature_rsa = DkimSigner::from_key(pk_rsa)
        .domain("example.com")
        .selector("default")
        .headers(["From", "To", "Subject"])
        .sign(RFC5322_MESSAGE.as_bytes())
        .unwrap();

    // Sign an e-mail message using ED25519-SHA256
    let pk_ed = Ed25519Key::from_bytes(
        &base64_decode(ED25519_PUBLIC_KEY.as_bytes()).unwrap(),
        &base64_decode(ED25519_PRIVATE_KEY.as_bytes()).unwrap(),
    )
    .unwrap();
    let signature_ed = DkimSigner::from_key(pk_ed)
        .domain("example.com")
        .selector("default-ed")
        .headers(["From", "To", "Subject"])
        .sign(RFC5322_MESSAGE.as_bytes())
        .unwrap();    

    // Print the message including both signatures to stdout
    println!(
        "{}{}{}",
        signature_rsa.to_header(),
        signature_ed.to_header(),
        RFC5322_MESSAGE
    );

ARC Chain Verification

    // Create a resolver using Cloudflare DNS
    let resolver = Resolver::new_cloudflare_tls().unwrap();

    // Parse message
    let authenticated_message = AuthenticatedMessage::parse(RFC5322_MESSAGE.as_bytes()).unwrap();

    // Validate ARC chain
    let result = resolver.verify_arc(&authenticated_message).await;

    // Make sure ARC passed verification
    assert_eq!(result.result(), &DkimResult::Pass);

ARC Chain Sealing

    // Create a resolver using Cloudflare DNS
    let resolver = Resolver::new_cloudflare_tls().unwrap();

    // Parse message to be sealed
    let authenticated_message = AuthenticatedMessage::parse(RFC5322_MESSAGE.as_bytes()).unwrap();

    // Verify ARC and DKIM signatures
    let arc_result = resolver.verify_arc(&authenticated_message).await;
    let dkim_result = resolver.verify_dkim(&authenticated_message).await;

    // Build Authenticated-Results header
    let auth_results = AuthenticationResults::new("mx.mydomain.org")
        .with_dkim_result(&dkim_result, "[email protected]")
        .with_arc_result(&arc_result, "127.0.0.1".parse().unwrap());

    // Seal message
    if arc_result.can_be_sealed() {
        // Seal the e-mail message using RSA-SHA256
        let pk_rsa = RsaKey::<Sha256>::from_pkcs1_pem(RSA_PRIVATE_KEY).unwrap();
        let arc_set = ArcSealer::from_key(pk_rsa)
            .domain("example.org")
            .selector("default")
            .headers(["From", "To", "Subject", "DKIM-Signature"])
            .seal(&authenticated_message, &auth_results, &arc_result)
            .unwrap();

        // Print the sealed message to stdout
        println!("{}{}", arc_set.to_header(), RFC5322_MESSAGE)
    } else {
        eprintln!("The message could not be sealed, probably an ARC chain with cv=fail was found.")
    }

SPF Policy Evaluation

    // Create a resolver using Cloudflare DNS
    let resolver = Resolver::new_cloudflare_tls().unwrap();

    // Verify HELO identity
    let result = resolver
        .verify_spf_helo("127.0.0.1".parse().unwrap(), "gmail.com", "my-local-domain.org")
        .await;
    assert_eq!(result.result(), SpfResult::Fail);

    // Verify MAIL-FROM identity
    let result = resolver
        .verify_spf_sender("::1".parse().unwrap(), "gmail.com", "my-local-domain.org", "[email protected]")
        .await;
    assert_eq!(result.result(), SpfResult::Fail);

DMARC Policy Evaluation

    // Create a resolver using Cloudflare DNS
    let resolver = Resolver::new_cloudflare_tls().unwrap();

    // Verify DKIM signatures
    let authenticated_message = AuthenticatedMessage::parse(RFC5322_MESSAGE.as_bytes()).unwrap();
    let dkim_result = resolver.verify_dkim(&authenticated_message).await;

    // Verify SPF MAIL-FROM identity
    let spf_result = resolver
        .verify_spf_sender("::1".parse().unwrap(), "example.org", "my-local-domain.org", "[email protected]")
        .await;

    // Verify DMARC
    let dmarc_result = resolver
        .verify_dmarc(
            &authenticated_message,
            &dkim_result,
            "example.org",
            &spf_result,
            |domain| psl::domain_str(domain).unwrap_or(domain),
        )
        .await;
    assert_eq!(dmarc_result.dkim_result(), &DmarcResult::Pass);
    assert_eq!(dmarc_result.spf_result(), &DmarcResult::Pass);

More examples available under the examples directory.

Testing & Fuzzing

To run the testsuite:

 $ cargo test

To fuzz the library with cargo-fuzz:

 $ cargo +nightly fuzz run mail_auth

Conformed RFCs

DKIM

• RFC 6376 - DomainKeys Identified Mail (DKIM) Signatures
• RFC 6541 - DomainKeys Identified Mail (DKIM) Authorized Third-Party Signatures
• RFC 6651 - Extensions to DomainKeys Identified Mail (DKIM) for Failure Reporting
• RFC 8032 - Edwards-Curve Digital Signature Algorithm (EdDSA)
• RFC 4686 - Analysis of Threats Motivating DomainKeys Identified Mail (DKIM)
• RFC 5016 - Requirements for a DomainKeys Identified Mail (DKIM) Signing Practices Protocol
• RFC 5585 - DomainKeys Identified Mail (DKIM) Service Overview
• RFC 5672 - DomainKeys Identified Mail (DKIM) Signatures -- Update
• RFC 5863 - DomainKeys Identified Mail (DKIM) Development, Deployment, and Operations
• RFC 6377 - DomainKeys Identified Mail (DKIM) and Mailing Lists

SPF

• RFC 7208 - Sender Policy Framework (SPF)
• RFC 6652 - Sender Policy Framework (SPF) Authentication Failure Reporting Using the Abuse Reporting Format

DMARC

• RFC 7489 - Domain-based Message Authentication, Reporting, and Conformance (DMARC)
• RFC 8617 - The Authenticated Received Chain (ARC) Protocol
• RFC 8601 - Message Header Field for Indicating Message Authentication Status
• RFC 8616 - Email Authentication for Internationalized Mail
• RFC 7960 - Interoperability Issues between Domain-based Message Authentication, Reporting, and Conformance (DMARC) and Indirect Email Flows

ARF

• RFC 5965 - An Extensible Format for Email Feedback Reports
• RFC 6430 - Email Feedback Report Type Value: not-spam
• RFC 6590 - Redaction of Potentially Sensitive Data from Mail Abuse Reports
• RFC 6591 - Authentication Failure Reporting Using the Abuse Reporting Format
• RFC 6650 - Creation and Use of Email Feedback Reports: An Applicability Statement for the Abuse Reporting Format (ARF)

SMTP TLS Reporting

• RFC 8460 - SMTP TLS Reporting

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Copyright

Copyright (C) 2020-2023, Stalwart Labs Ltd.