Require email address for billing and shipping addresses

[annastreet]

How can I create a field under shipping and billing information that requires an email address? Currently the only email address that displays is the one of the person placing the order, however our orders are placed by sales reps who enter orders for other customers and we would like the customers' email so we can communicate directly with them.

[stevesh]

Could the sales rep just enter the customer's address in the Comments box ?