Hard drives from the laptop can be destroyed, as well we all know now. But offsite storage is required, and to keep them for many years, many times at least 10 years, is the norm, sometimes longer. Wherever the email server for the IRS is located is where you’ll find backups of every email she’s written.
http://www.freerepublic.com/focus/news/3170849/posts?page=19#19
Post shows that as early as 2007 IRS was moving away from tape as storage medium.