Fitzgerald's letter says that "we have learned that not all email of the Office of Vice President and the Executive Office of President for certain time periods in 2003 was preserved through the normal archiving process on the White House computer system."
Fitzgerald is not saying the email was destroyed, only that it was not preserved through the normal archiving process on the White House computer system. That may mean the email was destroyed, or it may mean that Fitzgerald’s evidence recovery team has recovered the email in question. There is no way to know.
In scandal after scandal the attempted deletion and evidence recovery of email has played a crucial role in litigation. Now is the time to learn about email and records management.
NCC-AIIM Educational Seminar
Enabling Information Sharing with Enterprise Content Management
Susan Miller's execellent summary.