Mailing charge (7)
I believe the answer is:
postage
'mailing charge' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for postage that I've seen before include "Charge for 23 Acrosses" , "Mailing cost" , "Cost to send a mail item" , "Cost of corresponding" , "Money charged for delivery" .)