You can export and import invoices, although the detail in these would be minimal. There isn’t a “move from one account to another” option as each account is independent from another.
The receipt hub allows you to create invoices on the go. This would take you through the files in your receipt hub (the ones imported from emailing in or from Dropbox for example), and allow you to enter the supplier name, reference, value and even mark as paid if you wish.
The filter on the email may not be the best idea as the email would need to come from you. It may certainly work, but just double check as some email providers use the original senders address.