Default mail account for all outgoing messages

[Justin Brown - SYNACS]

I've been asked to control the flow of mail in an Outlook 2003/
Exchange 2003 environment. Several of the Outlook clients are set up
with the following:

- Microsoft Exchange Server account
- One or more POP3/SMTP accounts

What I'm wondering is if there is a way to configure Outlook to send
ALL messages out through a specific account, i.e. Exchange, even if
the user selects "Accounts -> POP3 account name" in the New Message
window.

Would unchecking "Mail Setup -> Send/Receive -> All Accounts -> Send
mail items" for the POP3 accounts do it, or would those messages then
sit in the Outbox indefinitely. Part of this is me thinking out loud
=].

TIA...