Edit: small mistake. The initial request did come from Congress and went through the State Department. It was not a subpoena though, that came later.
Edit 2: Since it was clear to some, the reddit post was dated July 24th, 2014. That's 7 months, prior to the first subpoena.
“I’ve done quite a bit already in the last few months related to this. Her team had me do a bunch of exports and email filters and cleanup to provide a PST [personal storage file] of all of HRC’s emails to/from any .gov addresses,” Combetta wrote. [0]
Exporting email and filtering it, but only for .gov addresses(?).. I would imagine that whoever subpoenaed those mails was requesting not just .gov communication, and I can't help but think that these sort of actions are suggestive of some deeper cleanup activity.
[0] http://dailycaller.com/2016/09/19/computer-tech-who-asked-ho...
You don't redact email addresses when you are subpoenaed by the f'ing FBI.
edit: My bad, it was the House Select Committee on Benghazi (July 2014). The FBI didn't take custody of the server until August 2015.