They were subpoenaed by Congress, but not until March 4, 2015. The initial request for emails was made by the State Department.

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.