Mail off to Peruvian capital (4)
I believe the answer is:
lima
'peruvian capital' is the definition.
(I've seen this before)
'mail off' is the wordplay.
'off' indicates an anagram.
'mail' with letters rearranged gives 'LIMA'.
'to' acts as a link.
(Other definitions for lima that I've seen before include "Peruvian capital" , "distant city" , "Mail to capital of Peru" , "Mail to Peru'd capital" , "Send mail out to S America" .)