Ask Powell and Rove.
"Former Secretary of State Colin Powell said he kept two computers to send and receive emails while he was in the position.
During on an appearance on NBC's Meet the Press on Sunday, Powell said he used one computer for sending sensitive material and a second for less important communications.
"I had a secure State Department machine for secure material and I had a laptop that I could use for email. I would email relatives, friends, but I would also email in the department," he said."
"Not long after George W. Bush assumed the presidency in 2001, Rove, his top political aide, set up a private email server for use in the White House. The stated purpose of the system — the primary domain name on which was gwb43.com — was that it would be used exclusively for the sort of political correspondence that Bush and Rove were not permitted to do on the taxpayer’s dime."
"During the investigation, it came to light that Rove’s server had been used to send official, non-political emails — correspondence that was required by law to be preserved under the Presidential Records Act."
"On April 12, 2007, Rove’s operation admitted that it had deleted at least 5 million emails from the server. In December 2009, technicians who had examined the server reported that the number of emails that had been deleted was far greater — 22 million."