Second postie helping to identify address (7)
I believe the answer is:
oration
'address' is the definition.
(I know that oration is a type of oratory)
'second postie helping' is the wordplay.
'second postie' becomes 'o' (2nd letter of 'postie').
'helping' becomes 'ration' (a ration is a serving or helping).
'o'+'ration'='ORATION'
'to identify' is the link.
(Other definitions for oration that I've seen before include "Major speech" , "Power of speech" , "An eloquent speech" , "A formal or public speech" , "Type 16 [OF SPEECH]" .)