I am a network administrator and have come across a problem regarding MS Outlook for MAC. The user has their own account already added to their outlook. They have requested that a group mailbox could be added. I set it up in exchange gave the appropriate permissions, then added the mailbox in the user's outlook. It worked fine, they can send with the alias that was created. The only problem is, when they send from the alias (Lets call it firstname.lastname@example.org) It shows up in their personal (email@example.com) sent items folder. Is there a way to change it so that it shows up in the firstname.lastname@example.org's sent items folder?
On the client-side, no.
If there is some reason that you can't update your Exchange server, then you could get around this on the client-side with a bit of work. If the senders BCC the email@example.com address when sending mail from that account, you could have a server-side rule on firstname.lastname@example.org which automatically moves mail that is BCCed to email@example.com to the Sent Items folder. This isn't by any means a perfect solution, but it might work until you can update your Exchange server.