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 accounting@mycompany.com for invoices, Sales@mycompany.com for estimates and support@mycompany.com 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 me@mycompany.com or from the global setup for sales. (sales@mycompany.com)