Where did the order go?

Email is great. It's elevated the efficiency of 'inside' sales people tremondously. But is has created some new problems. Suppose an important sales message, like a PO or a quote-request, is sent to the email account of someone who is out for a day or more. Like most people, I don't turn on my email 'vacation message' unless I'm out for more than three days.

Here is a solution one purchasing agent recently used as part of his email text:

PLEASE REPLY TO THIS EMAIL TO CONFIRM RECEIPT OF THE RFP. Should a reply not be received by Friday Oct 8 at 1:00PM I will send a paper copy via fax to your number in order to ensure timely receipt of the RFP.

What else can a sales team do to help make sure POs and RFPs aren't left ignored for days? This is one reason people feel compelled to check their email even while on vacation. Does it have to be that way? Any suggestions? What works for you?