Finally sub-postmaster is taking on Post Office and head of Fujitsu following exploitative situations (3-4)

'finally sub-postmaster is' is the definition.
I can't tell whether this definition defines the answer.

'on post office and head of fujitsu following exploitative situations' is the wordplay.
'on' is an insertion indicator (as in clothing 'on' a person).
'post office' becomes 'po' (abbreviation).
'and' says to put letters next to each other.
'head of' says to take the initial letters.
'exploitative situations' becomes 'ris' (I can't justify this - if you can you should give a lot more credence to this answer).
The first letters of 'fujitsu following' is 'ff'.
'po'+'ff'='poff'
'poff' placed into 'ris' is 'RIP-OFFS'.

'taking' is the link.

Can you help me to learn more?