A question about an invoice? Ask it on the document itself, not in a long email chain. Open the document, and write a comment.
Type the at sign, and pick a colleague. Send it. Maria gets an email, and a notification that opens this exact document.
She replies in the same thread, so the answer stays with the invoice. Finally, decide who can do what. Role permissions are managed by super admins.
For example, bookkeepers can upload and comment, but only accountants can register invoices. Next up: mailbox intake, and multi-page PDFs.