“Send on behalf” IE 5.5 question

Good day all,

I currently have Exchange 5.5 using Microsoft Outlook 2000 with winNT Server. I need to send a list using our sales@yada.com account. I get the “cannot send on behalf” error. I go into exchange, click on Hidden, and see a sales distribution list, but no sales mailbox. I try to create a sales mailbox, but it says it already exists. I can receive emails that are addressed to sales because I’m apart of the distribution list, but how can I get to delegate options in Outlook if I can’t access the account. Any help will greatly be appreciated.