Actually, you need a program that “wipes” the drive completely clear to prevent people from snooping on the drive. I believe there are programs out there that allow you to rewrite every sector with a single type of data (government rules require you do re-write every sector three times).
Umm, data can be recovered after as many as thirty-five such rewrites.
In addition to the 16 pound sledge, I recommend a 50 gallon drum, a few gallons of diesel oil, a blow torch, and raking the resulting ashes through a gravel parking lot.
Of course, your actual mileage may vary.
From a National Security standpoint, I would prefer that the White House NOT have a state of the art email archive, backup, and retrieval system. That would be one h*ll of a target for our cyber enemies to exploit.