feat(rust): implement mailer-core and mailer-security crates with CLI

Rust migration Phase 1 — implements real functionality in the previously
stubbed mailer-core and mailer-security crates (38 passing tests).

mailer-core: Email/EmailAddress/Attachment types, RFC 5322 MIME builder,
email format validation with scoring, bounce detection (14 types, 40+
regex patterns), DSN status parsing, retry delay calculation.

mailer-security: DKIM signing (RSA-SHA256) and verification, SPF checking,
DMARC verification with public suffix list, DNSBL IP reputation checking
(10 default servers, parallel queries), all powered by mail-auth 0.7.

mailer-bin: Full CLI with validate/bounce/check-ip/verify-email/dkim-sign
subcommands plus --management mode for smartrust JSON-over-stdin/stdout IPC.

rust/crates/mailer-security/src/ip_reputation.rs

@@ -0,0 +1,280 @@
+use hickory_resolver::TokioResolver;
+use serde::{Deserialize, Serialize};
+use std::net::{IpAddr, Ipv4Addr};
+
+use crate::error::Result;
+
+/// Default DNSBL servers to check, same as the TypeScript IPReputationChecker.
+pub const DEFAULT_DNSBL_SERVERS: &[&str] = &[
+    "zen.spamhaus.org",
+    "bl.spamcop.net",
+    "b.barracudacentral.org",
+    "spam.dnsbl.sorbs.net",
+    "dnsbl.sorbs.net",
+    "cbl.abuseat.org",
+    "xbl.spamhaus.org",
+    "pbl.spamhaus.org",
+    "dnsbl-1.uceprotect.net",
+    "psbl.surriel.com",
+];
+
+/// Result of a DNSBL check.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct DnsblResult {
+    /// IP address that was checked.
+    pub ip: String,
+    /// Number of DNSBL servers that list this IP.
+    pub listed_count: usize,
+    /// Names of DNSBL servers that list this IP.
+    pub listed_on: Vec<String>,
+    /// Total number of DNSBL servers checked.
+    pub total_checked: usize,
+}
+
+/// Result of a full IP reputation check.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct ReputationResult {
+    /// Reputation score: 0 (worst) to 100 (best).
+    pub score: u8,
+    /// Whether the IP is considered spam source.
+    pub is_spam: bool,
+    /// IP address that was checked.
+    pub ip: String,
+    /// DNSBL results.
+    pub dnsbl: DnsblResult,
+    /// Heuristic IP type classification.
+    pub ip_type: IpType,
+}
+
+/// Heuristic IP type classification.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "lowercase")]
+pub enum IpType {
+    Residential,
+    Datacenter,
+    Proxy,
+    Tor,
+    Vpn,
+    Unknown,
+}
+
+/// Risk level based on reputation score.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum RiskLevel {
+    /// Score < 20
+    High,
+    /// Score 20-49
+    Medium,
+    /// Score 50-79
+    Low,
+    /// Score >= 80
+    Trusted,
+}
+
+/// Get the risk level for a reputation score.
+pub fn risk_level(score: u8) -> RiskLevel {
+    match score {
+        0..=19 => RiskLevel::High,
+        20..=49 => RiskLevel::Medium,
+        50..=79 => RiskLevel::Low,
+        _ => RiskLevel::Trusted,
+    }
+}
+
+/// Check an IP against DNSBL servers.
+///
+/// * `ip` - The IP address to check (must be IPv4)
+/// * `dnsbl_servers` - DNSBL servers to query (use `DEFAULT_DNSBL_SERVERS` for defaults)
+/// * `resolver` - DNS resolver to use
+pub async fn check_dnsbl(
+    ip: IpAddr,
+    dnsbl_servers: &[&str],
+    resolver: &TokioResolver,
+) -> Result<DnsblResult> {
+    let ipv4 = match ip {
+        IpAddr::V4(v4) => v4,
+        IpAddr::V6(_) => {
+            // IPv6 DNSBL is less common; return clean result
+            return Ok(DnsblResult {
+                ip: ip.to_string(),
+                listed_count: 0,
+                listed_on: Vec::new(),
+                total_checked: 0,
+            });
+        }
+    };
+
+    let reversed = reverse_ipv4(ipv4);
+    let total = dnsbl_servers.len();
+
+    // Query all DNSBL servers in parallel
+    let mut handles = Vec::with_capacity(total);
+    for &server in dnsbl_servers {
+        let query = format!("{}.{}", reversed, server);
+        let resolver = resolver.clone();
+        let server_name = server.to_string();
+        handles.push(tokio::spawn(async move {
+            match resolver.lookup_ip(&query).await {
+                Ok(_) => Some(server_name), // IP is listed
+                Err(_) => None,             // IP is not listed (NXDOMAIN)
+            }
+        }));
+    }
+
+    let mut listed_on = Vec::new();
+    for handle in handles {
+        match handle.await {
+            Ok(Some(server)) => listed_on.push(server),
+            _ => {}
+        }
+    }
+
+    Ok(DnsblResult {
+        ip: ip.to_string(),
+        listed_count: listed_on.len(),
+        listed_on,
+        total_checked: total,
+    })
+}
+
+/// Full IP reputation check: DNSBL + heuristic classification + scoring.
+pub async fn check_reputation(
+    ip: IpAddr,
+    dnsbl_servers: &[&str],
+    resolver: &TokioResolver,
+) -> Result<ReputationResult> {
+    let dnsbl = check_dnsbl(ip, dnsbl_servers, resolver).await?;
+    let ip_type = classify_ip(ip);
+
+    // Scoring: start at 100
+    let mut score: i16 = 100;
+
+    // Subtract 10 per DNSBL listing
+    score -= (dnsbl.listed_count as i16) * 10;
+
+    // Subtract 30 for suspicious IP types
+    match ip_type {
+        IpType::Proxy | IpType::Tor | IpType::Vpn => {
+            score -= 30;
+        }
+        _ => {}
+    }
+
+    let score = score.clamp(0, 100) as u8;
+    let is_spam = score < 50;
+
+    Ok(ReputationResult {
+        score,
+        is_spam,
+        ip: ip.to_string(),
+        dnsbl,
+        ip_type,
+    })
+}
+
+/// Reverse IPv4 octets for DNSBL queries: "1.2.3.4" -> "4.3.2.1".
+fn reverse_ipv4(ip: Ipv4Addr) -> String {
+    let octets = ip.octets();
+    format!("{}.{}.{}.{}", octets[3], octets[2], octets[1], octets[0])
+}
+
+/// Heuristic IP type classification based on well-known prefix ranges.
+/// Same heuristics as the TypeScript IPReputationChecker.
+fn classify_ip(ip: IpAddr) -> IpType {
+    let ip_str = ip.to_string();
+
+    // Known Tor exit node prefixes
+    if ip_str.starts_with("171.25.")
+        || ip_str.starts_with("185.220.")
+        || ip_str.starts_with("95.216.")
+    {
+        return IpType::Tor;
+    }
+
+    // Known VPN provider prefixes
+    if ip_str.starts_with("185.156.") || ip_str.starts_with("37.120.") {
+        return IpType::Vpn;
+    }
+
+    // Known proxy prefixes
+    if ip_str.starts_with("34.92.") || ip_str.starts_with("34.206.") {
+        return IpType::Proxy;
+    }
+
+    // Major cloud provider prefixes (datacenter)
+    if ip_str.starts_with("13.")
+        || ip_str.starts_with("35.")
+        || ip_str.starts_with("52.")
+        || ip_str.starts_with("34.")
+        || ip_str.starts_with("104.")
+    {
+        return IpType::Datacenter;
+    }
+
+    IpType::Residential
+}
+
+/// Validate an IPv4 address string.
+pub fn is_valid_ipv4(ip: &str) -> bool {
+    ip.parse::<Ipv4Addr>().is_ok()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_reverse_ipv4() {
+        let ip: Ipv4Addr = "1.2.3.4".parse().unwrap();
+        assert_eq!(reverse_ipv4(ip), "4.3.2.1");
+
+        let ip: Ipv4Addr = "192.168.1.100".parse().unwrap();
+        assert_eq!(reverse_ipv4(ip), "100.1.168.192");
+    }
+
+    #[test]
+    fn test_classify_ip() {
+        assert_eq!(
+            classify_ip("171.25.193.20".parse().unwrap()),
+            IpType::Tor
+        );
+        assert_eq!(
+            classify_ip("185.156.73.1".parse().unwrap()),
+            IpType::Vpn
+        );
+        assert_eq!(
+            classify_ip("34.92.1.1".parse().unwrap()),
+            IpType::Proxy
+        );
+        assert_eq!(
+            classify_ip("52.0.0.1".parse().unwrap()),
+            IpType::Datacenter
+        );
+        assert_eq!(
+            classify_ip("203.0.113.1".parse().unwrap()),
+            IpType::Residential
+        );
+    }
+
+    #[test]
+    fn test_risk_level() {
+        assert_eq!(risk_level(10), RiskLevel::High);
+        assert_eq!(risk_level(30), RiskLevel::Medium);
+        assert_eq!(risk_level(60), RiskLevel::Low);
+        assert_eq!(risk_level(90), RiskLevel::Trusted);
+    }
+
+    #[test]
+    fn test_is_valid_ipv4() {
+        assert!(is_valid_ipv4("1.2.3.4"));
+        assert!(is_valid_ipv4("255.255.255.255"));
+        assert!(!is_valid_ipv4("999.999.999.999"));
+        assert!(!is_valid_ipv4("not-an-ip"));
+    }
+
+    #[test]
+    fn test_default_dnsbl_servers() {
+        assert_eq!(DEFAULT_DNSBL_SERVERS.len(), 10);
+        assert!(DEFAULT_DNSBL_SERVERS.contains(&"zen.spamhaus.org"));
+    }
+}