That is dubious speculation, and I doubt that the Washington Post would engage in such tactics. It's more likely that the e-mail messages were illegally intercepted and that a criminal violation of the Electronic Communications Privacy Act occurred.
The best way to find out is to file a lawsuit against the John Doe who apparently violated the ECPA and issue the subpoenas.
Schedule a sworn deposition from "MD4Bush" and ask him if he is the same person involved in the original communications, and is the same person who posted a couple of days ago, and who might have been in a position to access those messages without his knowledge, and whether or not he authorized the release of the private messages to any third parties, and what was the identity of those third parties, and whether those third parties passed the private messages to others, etc.
There are a bunch of questions that MD4Bush needs to answer, and a good attorney will only need a few hours with him to obtain his statement. Then things can proceed from there.
This is a whale of story for anyone who can nail the guilty party.
Explain this "more likely"...and..."illegally intercepted"....does not follow Occam's Razor...