Add optional inbound relay (backup-MX) behind INBOUND_RELAY_ENABLE.

Port 25 accepts only configured domains and listed recipients, then forwards to an upstream; the outbound path is unchanged when the flag is off.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/store/inbound_test.go

@@ -0,0 +1,101 @@
+package store
+
+import (
+	"errors"
+	"testing"
+)
+
+func TestInboundDomainCRUD(t *testing.T) {
+	st := openTestStore(t)
+
+	d, err := st.AddInboundDomain("lists.example.com")
+	if err != nil {
+		t.Fatalf("AddInboundDomain: %v", err)
+	}
+	if d.ID == 0 || d.Name != "lists.example.com" || d.RecipientMode != RecipientModeList {
+		t.Fatalf("unexpected domain: %+v", d)
+	}
+	if d.Port != 25 || d.TLSMode != TLSModeMay || d.Host != "" {
+		t.Fatalf("unexpected default transport: %+v", d)
+	}
+
+	if _, err := st.AddInboundDomain("lists.example.com"); !errors.Is(err, ErrInboundDomainExists) {
+		t.Fatalf("duplicate error = %v, want ErrInboundDomainExists", err)
+	}
+
+	if err := st.UpdateInboundTransport(d.ID, "10.0.0.8", 25, TLSModeEncrypt); err != nil {
+		t.Fatalf("UpdateInboundTransport: %v", err)
+	}
+	addrs := []string{"staff@lists.example.com", "postmaster@lists.example.com"}
+	if err := st.UpdateInboundRecipients(d.ID, RecipientModeList, addrs); err != nil {
+		t.Fatalf("UpdateInboundRecipients: %v", err)
+	}
+
+	got, err := st.GetInboundDomain(d.ID)
+	if err != nil {
+		t.Fatalf("GetInboundDomain: %v", err)
+	}
+	if got.Host != "10.0.0.8" || got.TLSMode != TLSModeEncrypt || got.RecipientCount != 2 {
+		t.Fatalf("get after update: %+v", got)
+	}
+	if len(got.Recipients) != 2 || got.Recipients[0] != "postmaster@lists.example.com" {
+		t.Fatalf("recipients not sorted: %v", got.Recipients)
+	}
+
+	list, err := st.ListInboundDomains()
+	if err != nil {
+		t.Fatalf("ListInboundDomains: %v", err)
+	}
+	if len(list) != 1 || list[0].RecipientCount != 2 {
+		t.Fatalf("list: %+v", list)
+	}
+
+	if err := st.UpdateInboundRecipients(d.ID, RecipientModeAny, nil); err != nil {
+		t.Fatalf("switch to any: %v", err)
+	}
+	got, err = st.GetInboundDomain(d.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got.RecipientMode != RecipientModeAny || got.RecipientCount != 0 || len(got.Recipients) != 0 {
+		t.Fatalf("any mode should clear the list: %+v", got)
+	}
+
+	if err := st.DeleteInboundDomain(d.ID); err != nil {
+		t.Fatalf("DeleteInboundDomain: %v", err)
+	}
+	assertCount(t, st, "inbound_domains", 0)
+	assertCount(t, st, "inbound_transports", 0)
+	assertCount(t, st, "inbound_recipients", 0)
+	if _, err := st.GetInboundDomain(d.ID); !errors.Is(err, ErrInboundDomainNotFound) {
+		t.Fatalf("Get after delete = %v, want ErrInboundDomainNotFound", err)
+	}
+}
+
+func TestInboundDomainNotFound(t *testing.T) {
+	st := openTestStore(t)
+	if _, err := st.GetInboundDomain(99); !errors.Is(err, ErrInboundDomainNotFound) {
+		t.Fatalf("GetInboundDomain(missing) = %v", err)
+	}
+	if err := st.UpdateInboundTransport(99, "10.0.0.1", 25, TLSModeNone); !errors.Is(err, ErrInboundDomainNotFound) {
+		t.Fatalf("UpdateInboundTransport(missing) = %v", err)
+	}
+	if err := st.DeleteInboundDomain(99); !errors.Is(err, ErrInboundDomainNotFound) {
+		t.Fatalf("DeleteInboundDomain(missing) = %v", err)
+	}
+}
+
+func TestInboundDeleteCascadesRecipients(t *testing.T) {
+	st := openTestStore(t)
+	d, err := st.AddInboundDomain("backup.example.net")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := st.UpdateInboundRecipients(d.ID, RecipientModeList, []string{"a@backup.example.net"}); err != nil {
+		t.Fatal(err)
+	}
+	if err := st.DeleteInboundDomain(d.ID); err != nil {
+		t.Fatal(err)
+	}
+	assertCount(t, st, "inbound_recipients", 0)
+}