feat(config): add hosted_domains for multi-domain hosting

.github/workflows/ci.yml

@@ -19,7 +19,7 @@ jobs:
 
     steps:
     - name: Checkout code
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
       with:
         submodules: recursive
 
@@ -57,7 +57,7 @@ jobs:
 
     steps:
     - name: Checkout code
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
 
     - name: Setup Pantry
       uses: home-lang/pantry/packages/action@main
@@ -83,7 +83,7 @@ jobs:
 
     steps:
     - name: Checkout code
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
 
     - name: Setup Zig
       uses: mlugg/setup-zig@v2
@@ -105,7 +105,7 @@ jobs:
 
     steps:
     - name: Checkout code
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
       with:
         submodules: recursive
 
@@ -164,7 +164,7 @@ jobs:
 
     steps:
     - name: Checkout code
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
       with:
         submodules: recursive
 

.github/workflows/deploy.yml

@@ -14,7 +14,7 @@ jobs:
 
     steps:
     - name: Checkout code
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
       with:
         submodules: recursive
 

.github/workflows/release.yml

@@ -27,7 +27,7 @@ jobs:
 
     steps:
     - name: Checkout code
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
       with:
         submodules: recursive
 
@@ -59,7 +59,7 @@ jobs:
 
     steps:
     - name: Checkout code
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
 
     - name: Set up Docker Buildx
       uses: docker/setup-buildx-action@v3
@@ -92,7 +92,7 @@ jobs:
 
     steps:
     - name: Checkout code
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
 
     - name: Extract version from tag
       id: version

.github/workflows/version.yml

@@ -26,7 +26,7 @@ jobs:
 
     steps:
     - name: Checkout code
-      uses: actions/checkout@v4
+      uses: actions/checkout@v6
       with:
         fetch-depth: 0
         token: ${{ secrets.GITHUB_TOKEN }}

packages/zig/src/config_test.zig

@@ -268,3 +268,73 @@ test "authentication configuration flags" {
 
     try testing.expectEqual(false, cfg_auth_off.enable_auth);
 }
+
+fn baseCfg(hostname: []const u8, hosted: []const []const u8) config.Config {
+    return .{
+        .host = "0.0.0.0",
+        .port = 2525,
+        .max_connections = 100,
+        .enable_tls = false,
+        .tls_cert_path = null,
+        .tls_key_path = null,
+        .enable_auth = true,
+        .max_message_size = 10 * 1024 * 1024,
+        .timeout_seconds = 300,
+        .data_timeout_seconds = 600,
+        .command_timeout_seconds = 300,
+        .greeting_timeout_seconds = 30,
+        .rate_limit_per_ip = 100,
+        .rate_limit_per_user = 200,
+        .rate_limit_cleanup_interval = 3600,
+        .max_recipients = 100,
+        .hostname = hostname,
+        .hosted_domains = hosted,
+        .webhook_url = null,
+        .webhook_enabled = false,
+        .enable_dnsbl = false,
+        .enable_greylist = false,
+        .enable_tracing = false,
+        .tracing_service_name = "mail",
+        .enable_json_logging = false,
+    };
+}
+
+test "isLocalDomain matches hostname exactly" {
+    const cfg = baseCfg("mail.stacksjs.com", &.{});
+    try testing.expect(cfg.isLocalDomain("mail.stacksjs.com"));
+}
+
+test "isLocalDomain matches parent of hostname" {
+    const cfg = baseCfg("mail.stacksjs.com", &.{});
+    try testing.expect(cfg.isLocalDomain("stacksjs.com"));
+}
+
+test "isLocalDomain matches an entry in hosted_domains" {
+    const extras = [_][]const u8{ "paweldregan.com", "example.org" };
+    const cfg = baseCfg("mail.stacksjs.com", &extras);
+    try testing.expect(cfg.isLocalDomain("paweldregan.com"));
+    try testing.expect(cfg.isLocalDomain("example.org"));
+}
+
+test "isLocalDomain is case-insensitive" {
+    const extras = [_][]const u8{"paweldregan.com"};
+    const cfg = baseCfg("mail.stacksjs.com", &extras);
+    try testing.expect(cfg.isLocalDomain("MAIL.Stacksjs.COM"));
+    try testing.expect(cfg.isLocalDomain("StacksJS.COM"));
+    try testing.expect(cfg.isLocalDomain("PaWeLdReGaN.com"));
+}
+
+test "isLocalDomain rejects unrelated domains" {
+    const extras = [_][]const u8{"paweldregan.com"};
+    const cfg = baseCfg("mail.stacksjs.com", &extras);
+    try testing.expect(!cfg.isLocalDomain("evil.example"));
+    try testing.expect(!cfg.isLocalDomain("notstacksjs.com"));
+    try testing.expect(!cfg.isLocalDomain(""));
+}
+
+test "isLocalDomain has no parent for single-label hostname" {
+    // "localhost" has no '.' so there's no parent to match
+    const cfg = baseCfg("localhost", &.{});
+    try testing.expect(cfg.isLocalDomain("localhost"));
+    try testing.expect(!cfg.isLocalDomain("host"));
+}

packages/zig/src/core/config.zig

@@ -47,6 +47,10 @@ pub const Config = struct {
     rate_limit_cleanup_interval: u64,
     max_recipients: usize,
     hostname: []const u8,
+    /// Additional domains this server accepts mail for, beyond `hostname`
+    /// and its parent. Populated from TOML `server.hosted_domains` (comma-
+    /// separated string) or env `SMTP_HOSTED_DOMAINS`.
+    hosted_domains: []const []const u8 = &.{},
     webhook_url: ?[]const u8,
     webhook_enabled: bool,
     enable_dnsbl: bool,
@@ -86,6 +90,22 @@ pub const Config = struct {
         if (self.webhook_url) |url| allocator.free(url);
         if (self.acme_email) |email| allocator.free(email);
         if (self.list_unsubscribe_url) |url| allocator.free(url);
+        for (self.hosted_domains) |domain| allocator.free(domain);
+        if (self.hosted_domains.len > 0) allocator.free(self.hosted_domains);
+    }
+
+    /// Returns true if `domain` is one this server accepts mail for:
+    /// `hostname`, the parent of `hostname` (e.g. `mail.X` accepts `X`),
+    /// or any entry in `hosted_domains`. Match is case-insensitive.
+    pub fn isLocalDomain(self: Config, domain: []const u8) bool {
+        if (std.ascii.eqlIgnoreCase(domain, self.hostname)) return true;
+        if (std.mem.indexOfScalar(u8, self.hostname, '.')) |dot_pos| {
+            if (std.ascii.eqlIgnoreCase(domain, self.hostname[dot_pos + 1 ..])) return true;
+        }
+        for (self.hosted_domains) |hosted| {
+            if (std.ascii.eqlIgnoreCase(domain, hosted)) return true;
+        }
+        return false;
     }
 
     /// Validates the configuration and returns detailed error messages
@@ -265,6 +285,31 @@ pub fn loadConfig(allocator: std.mem.Allocator, cli_args: args.Args) !Config {
     return cfg;
 }
 
+/// Parse a comma-separated list of domain names into an owned slice of
+/// allocator-owned strings. Empty entries and surrounding whitespace are
+/// trimmed; an empty input yields a zero-length slice.
+fn parseDomainList(allocator: std.mem.Allocator, raw: []const u8) ![]const []const u8 {
+    var list = std.ArrayList([]const u8).empty;
+    errdefer {
+        for (list.items) |item| allocator.free(item);
+        list.deinit(allocator);
+    }
+    var it = std.mem.splitScalar(u8, raw, ',');
+    while (it.next()) |part| {
+        const trimmed = std.mem.trim(u8, part, " \t\r\n");
+        if (trimmed.len == 0) continue;
+        const dup = try allocator.dupe(u8, trimmed);
+        errdefer allocator.free(dup);
+        try list.append(allocator, dup);
+    }
+    return list.toOwnedSlice(allocator);
+}
+
+fn freeDomainList(allocator: std.mem.Allocator, list: []const []const u8) void {
+    for (list) |entry| allocator.free(entry);
+    if (list.len > 0) allocator.free(list);
+}
+
 /// Determine which configuration profile to use
 fn determineProfile() config_profiles.Profile {
     if (env.get("SMTP_PROFILE")) |profile_str| {
@@ -304,6 +349,7 @@ fn loadDefaultsFromProfile(allocator: std.mem.Allocator, profile: config_profile
         .rate_limit_cleanup_interval = @as(u64, profile_config.rate_limit_window_seconds) * 60, // Convert to seconds
         .max_recipients = @intCast(profile_config.max_recipients),
         .hostname = try allocator.dupe(u8, "localhost"),
+        .hosted_domains = try allocator.alloc([]const u8, 0),
         .webhook_url = null,
         .webhook_enabled = false, // Only enable when URL is provided via env var
         .enable_dnsbl = false, // Not in profile config yet
@@ -348,6 +394,13 @@ fn applyEnvironmentVariables(allocator: std.mem.Allocator, cfg: *Config) !void {
         cfg.hostname = try allocator.dupe(u8, value);
     }
 
+    // SMTP_HOSTED_DOMAINS — comma-separated list of additional hosted domains
+    if (env.get("SMTP_HOSTED_DOMAINS")) |value| {
+        const parsed = try parseDomainList(allocator, value);
+        freeDomainList(allocator, cfg.hosted_domains);
+        cfg.hosted_domains = parsed;
+    }
+
     // SMTP_MAX_CONNECTIONS
     if (env.get("SMTP_MAX_CONNECTIONS")) |value| {
         cfg.max_connections = std.fmt.parseInt(usize, value, 10) catch cfg.max_connections;
@@ -569,6 +622,12 @@ fn applyConfigFile(allocator: std.mem.Allocator, cfg: *Config, path: []const u8)
             allocator.free(cfg.hostname);
             cfg.hostname = try allocator.dupe(u8, value);
         }
+        // Comma-separated string until the TOML parser supports arrays.
+        if (server.getString("hosted_domains")) |value| {
+            const parsed = try parseDomainList(allocator, value);
+            freeDomainList(allocator, cfg.hosted_domains);
+            cfg.hosted_domains = parsed;
+        }
         if (server.getInt("max_connections")) |value| {
             cfg.max_connections = @intCast(value);
         }

packages/zig/src/core/protocol.zig

@@ -672,19 +672,12 @@ pub const Session = struct {
             return;
         }
 
-        // Prevent open relay: unauthenticated clients can only send to local domain
+        // Prevent open relay: unauthenticated clients can only send to a local domain
+        // (hostname, its parent, or any entry in config.hosted_domains).
         if (!self.authenticated) {
             if (std.mem.indexOf(u8, addr, "@")) |at_pos| {
                 const recipient_domain = addr[at_pos + 1 ..];
-                // Check if recipient domain matches hostname or is the parent domain
-                // e.g. hostname "mail.stacksjs.com" should accept mail for "stacksjs.com"
-                const is_local = std.ascii.eqlIgnoreCase(recipient_domain, self.config.hostname) or blk: {
-                    if (std.mem.indexOf(u8, self.config.hostname, ".")) |dot_pos| {
-                        break :blk std.ascii.eqlIgnoreCase(recipient_domain, self.config.hostname[dot_pos + 1 ..]);
-                    }
-                    break :blk false;
-                };
-                if (!is_local) {
+                if (!self.config.isLocalDomain(recipient_domain)) {
                     self.logger.logSecurityEvent(self.remote_addr, "Relay access denied for unauthenticated sender");
                     try self.sendResponse(writer, 550, "5.7.1 Relay access denied", null);
                     return;
@@ -1357,18 +1350,12 @@ pub const Session = struct {
         const sender = self.mail_from orelse "unknown";
 
         for (self.rcpt_to.items) |rcpt| {
-            // Determine if recipient is local or external
-            // Compare against hostname and its parent domain (mail.stacksjs.com -> stacksjs.com)
-            const is_local = if (std.mem.indexOf(u8, rcpt, "@")) |at_pos| blk: {
-                const rcpt_domain = rcpt[at_pos + 1 ..];
-                if (std.mem.eql(u8, rcpt_domain, self.config.hostname)) break :blk true;
-                // Also check parent domain: if hostname is "mail.X", accept "X" as local
-                if (std.mem.indexOf(u8, self.config.hostname, ".")) |dot_pos| {
-                    const parent_domain = self.config.hostname[dot_pos + 1 ..];
-                    if (std.mem.eql(u8, rcpt_domain, parent_domain)) break :blk true;
-                }
-                break :blk false;
-            } else true;
+            // Determine if recipient is local or external. A bare address with
+            // no '@' is treated as local (legacy local-user delivery).
+            const is_local = if (std.mem.indexOf(u8, rcpt, "@")) |at_pos|
+                self.config.isLocalDomain(rcpt[at_pos + 1 ..])
+            else
+                true;
 
             if (is_local) {
                 // Local delivery: save to Maildir
@@ -1500,16 +1487,11 @@ pub const Session = struct {
 
             self.logger.info("Auto-forwarding from {s} to {s}", .{ username, forward_to });
 
-            // Check if forward target is a local address
-            const is_local_forward = if (std.mem.indexOf(u8, forward_to, "@")) |at_pos| blk: {
-                const fwd_domain = forward_to[at_pos + 1 ..];
-                if (std.mem.eql(u8, fwd_domain, self.config.hostname)) break :blk true;
-                if (std.mem.indexOf(u8, self.config.hostname, ".")) |dot_pos| {
-                    const parent_domain = self.config.hostname[dot_pos + 1 ..];
-                    if (std.mem.eql(u8, fwd_domain, parent_domain)) break :blk true;
-                }
-                break :blk false;
-            } else true;
+            // Check if forward target is a local address.
+            const is_local_forward = if (std.mem.indexOf(u8, forward_to, "@")) |at_pos|
+                self.config.isLocalDomain(forward_to[at_pos + 1 ..])
+            else
+                true;
 
             if (is_local_forward) {
                 // Local forward: save directly to recipient's mailbox