This small modification will help you to improve user expereince when out of stock message is displayed to customer. If user add more items than available stock.
You need to edit the common.ini language file locate here;
you should find “InvLevelBelowOrderQty =” around line number 103 and edit this entry as follows, please note that :product will be replaced with currently viewing product name on email subject
InvLevelBelowOrderQty = “We don’t have enough :product (s) stock on hand for the quantity you selected. Please <blink><a href=’mailto:firstname.lastname@example.org ?subject=Out of stock item – :product’>email</a></blink> us for an estimated delivery date.”