The code around sender warnings due to banned content is somewhat peculiar.
For many constant confvars like $final_banned_destiny there are more generic confvars like %final_destiny_maps_by_ccat. The latter, as many other maps, is by recipient at some point. The map %warnsender_by_ccat is not. Its use is marked as deprecated, and it is not a clean generalization of $warnbannedsender. The combination of > $warnbannedsender = 1; > $final_banned_destiny = D_DISCARD; internally forces $final_banned_destiny to D_BOUNCE. One needs to know that for usage of %final_destiny_maps_by_ccat. As for the custom templates, the confvar %notify_sender_templ_by_ccat is also not per recipient, so your only chance to create recipient based sender notifications seems to be via macro expansion inside a common template for all recipients.