In the past the risk with email was mostly network sniffing during the transfer, which is somewhat low risk given who has access to backbone networks, and many systems have opportunistic TLS enabled, which is at least better than nothing.

However, after the Exchange hack, now we suddenly have to worry about all the stuff that’s stored in people’s mailboxes after delivery, which is likely a huge amount of data. I expect we’re going to see a huge wave of identity theft stemming from this.