post-free 
adjective & adverb British
Carried by post free of charge to the customer: [as adjective]: to arrange for a free survey fill in the post-free coupon [as adverb]: pamphlets were sent post-free to interested readers...
- This book is available by return of post (post-free) for £9.95 from our freepost address.
- To obtain Black Magic and Purple Passion at the special price of £12, post-free or for details about the International Black Plant Society contact us at te address below.
- All books ordered by telephone will be sent out post-free.