Outlook Mail Reply Being Sent from Wrong Account

In my Outlook app, I have
1. My default mail account
2. And a shared mailbox account added

I notice that when I reply to an email that's in the shared mail account inbox, it gets sent from my default account (the 'from' address shows the shared account name, but it's in my default account 'sent items' folder).

This happens on 'Old Outlook' on both MacOS and WindowsOS. Is there a way I can have the mail properly send from the shared account?

Thanks,
Bryan