The intention of the “email your receipts” facility is to let you (or specific members of your staff) forward in emails with receipts or invoices they have been sent by a supplier. It is not designed for the suppliers themselves to email invoices directly to QuickFile, since the routing of emails to the appropriate QuickFile account receipt hub is based on the “from” address - you might set up one of your suppliers to email your invoices in to receipts@quickfile.co.uk, but then nobody else who buys from the same supplier could do the same thing, since that supplier’s from address is already bound to your QuickFile account.
If you have a larger team than 10 staff who all need to inject invoices into the same QuickFile account then you might want to consider an alternative route such as a shared Dropbox folder (or my Google Drive equivalent) into which all your staff can drop files.