When it looks like these missing emails may have altered other investigations then it is time for a criminal probe into it:
Apparent gaps in White House e-mail archives coincide with dates in late 2003 and early 2004 when the administration was struggling to deal with the CIA leak investigation and the possibility of a congressional probe into Iraq intelligence failures.
Here is where the Plame case may come into play in this:
Among the times for which e-mail may not have been archived from Vice President Dick Cheney's office are four days in early October 2003, just as a federal probe was beginning into the leak of Valerie Plame's CIA identity, an inquiry that eventually ensnared Cheney's chief of staff.
Pretty convenient that emails would happen to be missing from those four days, and Melanie Sloan seems to concur: