Change default from address in when replying to e-mails

We recently migrated to Exchange 2003 from 5.5. We have several general e-mail boxes the many peaple use, for example Helpdesk. Since we migrated, when a user replies to a message from one of these mailboxes (ex. Helpdesk) the default “From” address shows up as whatever user account is associated with that mailbox. This use to not be. When we were still on 5.5 and we would reply to a e-mail from the the helpdesk mailbox the “From” address would show the actual sender not being from Helpdesk.

Is there a way to change this in exchange 2003 without actaully having to manually change the “From” field to yourself?