2 accounts in Outlook 2003

My clients are running XP SP2 w/Office 2k3; I have Exchange 2003 running. I have a user (John Doe)who has their exchange email account and who is also accessing a generic account “jobs@company.com.” Emails coming into John go to his inbox, and emails coming to Jobs go to the Jobs inbox, both set-up in his Outlook profile. But if John tries to reply to an email sent to Jobs, the email is being sent from JOHN, not from Jobs. How can I configure Outlook so that he can select an account to send the exchange emails from? John has an IMAP account too (can’t have multiple IMAP accts- so that option is out).