Just the subject line, who it is from and going to, plus the date - not the text... but still, if a source's Inbox is viewable without much difficulty, that in and of itself could be probable cause for warrants, or other bad mojo.
I was putting this out there primarily for the benefit of sources. As to whether it could make or break them, if their Inbox is basically viewable on demand, then this could be used as grounds for warrants or looking into other inboxes, laying down webs of connections, who seems to order how many times from who, who does anyone talk to... it wouldn't take long to lay down the whole map. That could make or break a lot of people.
Now whether they are doing this, or how much of a legal barrier needs to be overcome at each remove from the original subject of investigation, that's a matter of speculation.
But it seems obvious that if they put in an order with
Source@hushmail.com and that order gets filled, then they can have a warrant to look at that guy's InBox in about 10 minutes. (Which is to say that it is basically viewable on demand for sources who are not private). Then they can also probably get IP addresses of where the account was accessed from, and start going from there. Oh, Source'sBiggestCustomer@hushmail.com has 150 emails in
Source@hushmail.com's InBox... that's grounds to look at his InBox, IP's, and payment/registration info if the account is Advanced.
Or Source'sPowderConnection@hushmail.com,
or Source'sRemailer#1@hushmail.com, #2, #3...
So yeah, I think it is pretty serious.