Surely you know that those vouchers you give your clients for mailing ES payments are not addressed to an IRS facility.  Nor are Forms 941 with payments mailed to an IRS service center.  I know the guy is not your client, but why would he need to send a cashier's check?  When the private lockbox receives a check from the Beaver Creek, Blue Ball and Climax Federal Credit Union, how do they know where to apply it, if the voucher it came with goes astray?

Speaking of reasons IRS should not hire government contractors, this news just in:

An Internal Revenue Service (IRS) consultant was charged today with disclosing tax return information without authorization.

According to court documents, Charles Littlejohn, 38, of Washington, D.C., while working at the IRS as a government contractor, stole tax return information associated with a high-ranking government official (Public Official A) and disclosed it to a news organization (News Organization 1). Littlejohn also stole tax return information for thousands of the nation’s wealthiest individuals, and disclosed this tax return information to another news organization (News Organization 2).

Littlejohn is charged with one count of unauthorized disclosure of tax returns and return information. If convicted, he faces a maximum penalty of five years in prison.