[mannyv]

I suppose when you have a large corpus you start with as many browse points as you can. So maybe a list of the top senders, top recipients, recipient graphs.

I'd think by day would be next. Browse subjects by day, and word clouds for each message thread? The. Try to isolate topics discussed each day, then link the topics across days.

You should be able to click in and see the thread/messages/etc.

This is, at some level, how legal discovery stuff works from what I understand.

[DANmode]

The part you're missing here is having a clue about what's sensitive in geopolitics in the first place, so you have that place to work from.