I understand you want an emailing system to receive orders, Fill orders, and inform staff of orders that have been replied to.
I can create a program that will do this, I believe a program would be better for this kind of thing. A program allows more usability, allows things like copies and receipts and errors to be logged with ID's, Put into a data base. The program can be connected to a server VPN or internet, allowing it to exchange information from computer to computer whether they are linked or not, or whether they are linked to the internet or not.
The program would be $400 within 10 days. I will provide 5 days of bug support and error resolving and program editing, any further adjustments after this 5 days, will be at $15 an hour.