2 years is a ridiculously short time to "age out" email archives. Especially for an agency that takes longer than that to handle basic interactions. I just got a call last month from the IRS regarding the estate of a relative who passed in 2011. And the IRS claims they have the authority to go back six years for substantial errors so I'd expect them to be keeping their emails at least that long. More realistically, I'd expect them to keep their emails indefinitely. Storage is getting cheaper faster than email accumulates. What does the average person accumulate in a decade? 5 gigs? IRS has around 90,000 employees so that's 450,000 gigs of data give or take. Shit, I've got 32,000 gigs of storage 2' from me. I could expand that to 78,000 by swapping in bigger hard drives. And 144,000 by swapping in bigger drives and adding more ports. That's with stuff I could order from Newegg and assemble on the dining room table. If I went with real equipment, the only limit would be my wallet.
Last company I worked for, had been archiving email for years before I started and hadn't thrown out (or lost) a single email when I left 5 years later. If legal needed something from 2005, they'd give me the particulars and I'd plug them in and the system spit out a compilation of every message that met the specs. I also made an image of every employee's hard drive when they left the company before I put a fresh image on their computer. Just in case they'd stored something important on their local drive instead of their department's server. Only needed that a few times but the cost was so negligible we spent more on donuts and bagels than storing drive images.
Their failure to have a redundant, secure archive of such recent email is either intentional destruction or gross incompetence.