Maybe more computer sophisticated folks already were hip to this tactic, but I found the mechanics to be kind of clever.
From the AP:
"Petraeus and Broadwell apparently used a trick, known to terrorists and teenagers alike, to conceal their email traffic, one of the law enforcement officials said.
Rather than transmitting emails to the other's inbox, they composed at least some messages and instead of transmitting them, left them in a draft folder or in an electronic "dropbox," the official said. Then the other person could log onto the same account and read the draft emails there. This avoids creating an email trail that is easier to trace."
The Washington Post reports that this tactic has been used by al-Qaeda terrorists as far back as 2005.
The Post notes that using draft mode rather than hitting "send" on an email leaves less of an electronic trail. When messages are actually sent, " both accounts record the transmission as well as such metadata as the IP addresses on either end, something the two seemed to be seeking to avoid," the Post notes.
Between 20,000 and 30,000 pages of emails between Petraeus and Broadwell sent from 2010 to 2012 are currently under investigation, according to the AP.
Kind of ironic that a former general's downfall would result from not avoiding the draft . . . .