If checkboxes are cleared in "Settings for group "All Accounts"" (Under
Send/Receive Groups), how often does Outlook 2003 (Exchange 2003) check for
new mail?

Just below that are offline options and if they're cleared, there's no
checking at all, like in Outlook 2000.

Background. Two users are attempting to test this, but in a way that I don't
think is valid. They have an O2K client (CW) and an O2K3 client open at the
same time side by side (online) and are checking them side by side. O2K gets
messages immediately, O2K3, periodically (cached mode, apparently, with the
checkboxes cleared).