These handle different problems and shouldn't be forced into one tool. ERP handles the internal side: inventory, production, finance, purchase-to-sales-to-inventory—your company's own books. The part facing overseas buyers—inquiries come in, quotations go out, orders confirmed, PI issued, shipments arranged—is an external business process where both parties need to see the same document, confirm back and forth, and keep version records. Each has its own logic. ERP isn't good at "collaborating with external people." An external business system doesn't need to handle "internal accounting and inventory management." The sensible architecture is: external business flows—inquiries, quotations, documents—have their own system, with needed data synced to ERP afterward. Don't try to squeeze everything into one system, and don't keep patching things together with Email and Excel.