[otrs] Replies to internal mails are visible by customers

If an agent want to have someone internally within the company to have a look at a case, it is possible to forward the customer's posting as an internal mail. The internal mail is hidden from the customer. This is great! However the reply address to this mail is the queue reply address, and the reply to the internal mail is posted as an external mail, hence it is visible by the customer. Is it a way to configure OTRS so replies to internal mails are also handled as internal communication ? Regards, - Erik -