feat(protocols): trusted senders are not filed as spam, when the message proves its sender

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

services/protocols/internal/application/usecase/trusted_delivery_test.go

@@ -0,0 +1,100 @@
+package usecase
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"testing"
+
+	"github.com/google/uuid"
+
+	"lambdamail/protocols/internal/application/port"
+	"lambdamail/protocols/internal/domain/valueobject"
+)
+
+type fakeTrusted struct {
+	trusted map[string]bool
+	err     error
+}
+
+func (f *fakeTrusted) IsTrusted(_ context.Context, _ uuid.UUID, address string) (bool, error) {
+	return f.trusted[address], f.err
+}
+
+func deliverAsSpam(t *testing.T, trusted port.TrustedSenders, auth port.InboundAuthResult, envelope string) string {
+	t.Helper()
+	repo := &recordingMessageRepository{}
+	uc := NewProcessInboundEmailUseCase(nil, &capturingBlobStorage{}, repo)
+	uc.SetScanner(&stubScanner{result: &valueobject.ScanResult{Verdict: valueobject.ScanVerdictSpamJunk}})
+	uc.SetAuthenticator(&stubAuthenticator{result: auth})
+	if trusted != nil {
+		uc.SetTrustedSenders(trusted)
+	}
+	err := uc.Handle(context.Background(), ProcessInboundEmailInput{
+		Sender:             envelope,
+		Recipients:         []port.MailboxRecord{{ID: uuid.New()}},
+		RecipientAddresses: []string{"me@example.test"},
+		Body:               bytes.NewBufferString("From: Jenny <Jenny@Friend.test>\r\nSubject: re: hi\r\n\r\nbody"),
+	})
+	if err != nil {
+		t.Fatalf("Handle: %v", err)
+	}
+	return repo.persisted[0].TargetFolderName
+}
+
+var passDMARC = port.InboundAuthResult{SPF: "pass", DKIM: "pass", DMARC: "pass"}
+
+func TestTrustedSenderIsNotFiledAsSpam(t *testing.T) {
+	trusted := &fakeTrusted{trusted: map[string]bool{"jenny@friend.test": true}}
+	if got := deliverAsSpam(t, trusted, passDMARC, "jenny@friend.test"); got != "INBOX" {
+		t.Fatalf("a trusted, authenticated sender was filed in %q", got)
+	}
+}
+
+func TestUntrustedSenderStillGoesToJunk(t *testing.T) {
+	trusted := &fakeTrusted{trusted: map[string]bool{"someone@else.test": true}}
+	if got := deliverAsSpam(t, trusted, passDMARC, "jenny@friend.test"); got != "Junk" {
+		t.Fatalf("an untrusted sender was filed in %q", got)
+	}
+}
+
+// Writing a contact's address in From is all a spammer needs to do, so trust
+// only counts when the message proves it came from there.
+func TestForgedTrustedSenderStillGoesToJunk(t *testing.T) {
+	trusted := &fakeTrusted{trusted: map[string]bool{"jenny@friend.test": true}}
+	forged := port.InboundAuthResult{SPF: "fail", DKIM: "none", DMARC: "fail"}
+	if got := deliverAsSpam(t, trusted, forged, "bounce@spammer.test"); got != "Junk" {
+		t.Fatalf("a forged From reached the inbox: %q", got)
+	}
+}
+
+// SPF that passed for the spammer's own domain proves nothing about From.
+func TestSPFForAnotherDomainDoesNotProveFrom(t *testing.T) {
+	trusted := &fakeTrusted{trusted: map[string]bool{"jenny@friend.test": true}}
+	other := port.InboundAuthResult{SPF: "pass", DKIM: "none", DMARC: "none"}
+	if got := deliverAsSpam(t, trusted, other, "bounce@spammer.test"); got != "Junk" {
+		t.Fatalf("SPF for a different domain let a forged From in: %q", got)
+	}
+}
+
+// A domain with no DMARC record can still be proven by SPF for its own domain.
+func TestSPFForTheSameDomainProvesFrom(t *testing.T) {
+	trusted := &fakeTrusted{trusted: map[string]bool{"jenny@friend.test": true}}
+	spfOnly := port.InboundAuthResult{SPF: "pass", DKIM: "none", DMARC: "none"}
+	if got := deliverAsSpam(t, trusted, spfOnly, "mailer@friend.test"); got != "INBOX" {
+		t.Fatalf("SPF for the sender's own domain was not accepted: %q", got)
+	}
+}
+
+func TestLookupFailureLeavesTheMessageInJunk(t *testing.T) {
+	trusted := &fakeTrusted{trusted: map[string]bool{"jenny@friend.test": true}, err: errors.New("db down")}
+	if got := deliverAsSpam(t, trusted, passDMARC, "jenny@friend.test"); got != "Junk" {
+		t.Fatalf("a failed lookup let mail through: %q", got)
+	}
+}
+
+func TestWithoutTrustedSendersSpamGoesToJunk(t *testing.T) {
+	if got := deliverAsSpam(t, nil, passDMARC, "jenny@friend.test"); got != "Junk" {
+		t.Fatalf("filed in %q", got)
+	}
+}