Deliveries by agent including electronic stuff (8)

'stuff' is the definition.
(thesaurus)

'deliveries by agent including electronic' is the wordplay.
'deliveries' becomes 'over' (I've seen this before).
'by' says to put letters next to each other.
'agent' becomes 'fed' (fed is a kind of agent**).
'including' indicates putting letters inside.
'electronic' becomes 'e' (as in e-mail or e-books).
'fed' enclosing 'e' is 'feed'.
'over'+'feed'='OVERFEED'