It would be good to have the functionality that shows e-mail based on specific search criteria. Ideally a broad one that is capable of using fields and tags, but MVP would be to have a folder that allows a view on documents that contain tag an and b. Example. For example the option to tag a document with invoice [document tag], project, [status], [supplier]. In case you would like to have a view that shows all the invoices for projects, you create a folder that searches for tag "invoice", and tag "project". It is a simple example but it offers opportunities to better manage the e-mails.