The suppliers will receive your orders via email if the Email Order option is enabled in their settings page. To enable email via orders, navigate to Settings -> App Settings -> Zip Orders -> Suppliers. Select the supplier you want to send email orders to, and in the righthand-side of the page there is a field for Email ID and Email Order. Make sure the email is a valid email for that supplier and that there is a green check mark in the Email Order box. Now that supplier will receive an email every time you place an order with them!
Hope that helps.