Is that a smoking gun I smell? It turns out the IRS contracted with a company that provides email backup services starting in 2005. This first came to light in the Twitter feed of moregenr[ed. - researcher for the dearly departed Verum Serum blog], who noticed that the IRS appears on the client list of email archiving service provider Sonasoft.
This was was picked up by Peter Suderman of Reason, who writes:
The IRS had a contract with email backup service vendor Sonasoft starting in 2005,according to FedSpending.org, which lists the contract as being for “automatic data processing services.” Sonasoft’s motto is “email archiving done right,” and the companylists the IRS as a customer.
In 2009, Sonasoft even sent out a Tweet advertising its work for the IRS.