Log every intra-company communication, and if some communication was meant to go to department X, Y, Z, and it only went to X, Y, then a flag would be immediately raised to department Z's attention and whoever sent it.
Of course the personnel in department Z might review it but ignore it anyways, but at least now there's a paper trail of who's at fault.
An Exchange system already gets you 80% of the way there if you force all on-the-record communications via email.
I can imagine the brute-force approach:
Log every intra-company communication, and if some communication was meant to go to department X, Y, Z, and it only went to X, Y, then a flag would be immediately raised to department Z's attention and whoever sent it.
Of course the personnel in department Z might review it but ignore it anyways, but at least now there's a paper trail of who's at fault.
An Exchange system already gets you 80% of the way there if you force all on-the-record communications via email.