From the Associated Press:

Bin Laden’s system was built on discipline and trust. But it also left behind an extensive archive of email exchanges for the U.S. to scour. The trove of electronic records pulled out of his compound after he was killed last week is revealing thousands of messages and potentially hundreds of email addresses, the AP has learned.

Holed up in his walled compound in northeast Pakistan with no phone or Internet capabilities, bin Laden would type a message on his computer without an Internet connection, then save it using a thumb-sized flash drive. He then passed the flash drive to a trusted courier, who would head for a distant Internet cafe.

At that location, the courier would plug the memory drive into a computer, copy bin Laden’s message into an email and send it. Reversing the process, the courier would copy any incoming email to the flash drive and return to the compound, where bin Laden would read his messages offline.