We have a single group of technicians that handle requests for multiple accounts. I've set up the accounts with a custom e-mail address ( customer@myMSPcompany.com).  E-mails sent to this address show up in the account as they should. However, when a technician replies to the request, the From e-mail address that the customer sees is ( servicedeskfetchingmailbox@myMSPcompany.com).  

How can I have customers see emails from customer@myMSPcompany.com for these replies?

Any help would be greatly appreciated.