Former postman, one now living abroad (5)
I believe the answer is:
expat
'one now living abroad' is the definition.
(short for expatriate)
'former postman' is the wordplay.
'former' becomes 'ex'.
'postman' becomes 'pat' (children's TV character Postman Pat).
'ex'+'pat'='EXPAT'
(Other definitions for expat that I've seen before include "one working abroad" , "One living in foreign country" , "Emigre" , "Former countryman" , "overseas settler" .)