In an email response to a friendly note Mrs. Clinton sent dated Jan. 23, 2009, Mr. Powell said he used both a "personal computer" and a device he described as a "PDA"--likely short for "Personal Digital Assistant," the name used for early smartphone-like devices. Mrs. Clinton had sought Mr. Powell's advice for how to bring her BlackBerry smartphone along at the State Department, describing herself as an "addict."

The newly released emails appear to show Mr. Powell, who served as secretary of state between 2001 and 2005 under President George W. Bush, acknowledging he exchanged work-related emails with foreign leaders and State Department officials using a personal computer or by corresponding with the personal accounts of senior government staffers. The setup enabled Mr. Powell's correspondence to bypass the government's computer network, he said.

"I didn't have a BlackBerry. What I did do was have a personal computer that was hooked up to a private phone line (sounds ancient.) So I could communicate with a wide range of friends directly without it going through the State Department servers," Mr. Powell wrote to Mrs. Clinton, now the Democratic nominee for president.

"I even used it to do business with some foreign leaders and some of the senior folks in the Department on their personal email accounts. I did the same thing on the road in hotels," he said.