If I have my Outlook 2003 client is closed when the email is intended to be sent, will the email still be sent?
Is it a function of the Exchange Server or my Outlook 2003 client?
This depends if you are running your Outlook client in cached Exchange mode or not.
Cached Exchange mode: Outlook must be open for the delayed send to occur at the designated time.
Online mode: Outlook can be closed (and the PC even shut down) and delayed send will still work- it is stored and sent by the Exchange server.