Custom email sender for each module (Service, Invoice, Estimates)
Currently all email communication from RS comes from the same mailbox which means that a client responding to an invoice, estimate or a service ticket will get their response dumped into the service desk.
My suggestion is that each module have a customization setting to allow a different sender address. For example, I may provide email@example.com for invoices, Sales@mycompany.com for estimates and firstname.lastname@example.org for service.
A more advanced suggestion would be to have the option to send email as the logged in user. So I could send the estimate as from email@example.com or from the global setup for sales. (firstname.lastname@example.org)