“On the behalf of..” has disappeared

We use a generic help desk inbox that all of the IT staff has owner rights to. We would all send email by changing the “from” field to user “HelpDesk”. The emails when received would reflect, “persons name on the behalf of HelpDesk” We have moved to a new Exchange 2000 server and the “behalf of” no longer appears. Even thou we change the “from” field and it shows “HelpDesk” when sending email out the receipt of it reflects only the persons name. So responses go back to the sender as a person and not the generic HelpDesk inbox. No settings have been changed at the user Help Desk’s Inbox. Have used Microsoft’s Chat Support and articles 327000 & 328927 with no luck.