Are the emails inside the outbox folder stored locally on the machine where the mail was sent

I'm asking this question because I got curious about an email I'm sending from the office with Outlook using the Delay delivery option. When I searched for that mail at home to modify it on Outlook, I couldn't find it.

Are emails stuck inside the Outbox folder (as is the case of a Delay delivery email) local to the machine where they were sent? and if possible where are these mail stored physically (path to a file)?

Besides, if these emails are stored locally, does it mean that Outlook in this case is using POP protocol instead of IMAP (where emails would be synchronized from a remote server)?