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/infrastructure/postgres/trusted_senders.go

@@ -0,0 +1,32 @@
+package postgres
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/google/uuid"
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+// TrustedSenders reads the senders a mailbox trusts. The webmail writes them
+// through the auth service; delivery only ever asks.
+type TrustedSenders struct {
+	pool *pgxpool.Pool
+}
+
+func NewTrustedSenders(pool *pgxpool.Pool) *TrustedSenders {
+	return &TrustedSenders{pool: pool}
+}
+
+func (t *TrustedSenders) IsTrusted(ctx context.Context, mailboxID uuid.UUID, address string) (bool, error) {
+	var trusted bool
+	err := t.pool.QueryRow(ctx, `
+		SELECT EXISTS (
+			SELECT 1 FROM trusted_senders WHERE mailbox_id = $1 AND address = $2
+		)
+	`, mailboxID, address).Scan(&trusted)
+	if err != nil {
+		return false, fmt.Errorf("look up a trusted sender: %w", err)
+	}
+	return trusted, nil
+}