Degaussing? Oh No! know we need to understand hysteresis loops!
http://en.wikipedia.org/wiki/Hysteresis
in info tech people always said the last place you wanted to work was for the government - because in government budgeting, money has to be spent on what its allocated for - which meant the technology was always far, far behind the private sector
the irs e/mail servers were probably very old technology - so that data is probably gone from the irs
it will still be on the recipient servers though