Aaron,
You don't specify the type of mail server or which version of Outlook, but I can tell you what should work for Outlook 97/98 connecting to MS Exchange. You can hopefully adjust from there.
It is likely that Outlook is set up as if it were on a LAN (that's the default). This means it will automatically detect the connection state using a 30-second timeout and, if the server doesn't respond in that time, will assume that the network is "off-line."
In Outlook, click the menu Tools..Services. Click the item Microsoft Exchange Server and click the Properties button. There you will see if it is set to Automatically Detect the Connection State. You can either increase the amount of Seconds Until Server Connection Timeout, or you can change it to Manually Determine the Connection State, or both.
I recommend increasing the server timeout and see if that works. From the way you phrased your question, it seems that you want the situation to be transparent to the user, and increasing the server timeout is probably the way to go. For those who are using a dial-up connection from their houses, though, you'll want a much longer timeout value.
Good fortune,
Don
