Some of President Obama's political appointees, including the Cabinet secretary for the Health and Human Services Department, are using secret government email accounts they say are necessary to prevent their inboxes from being overwhelmed with unwanted messages, according to a review by The Associated Press.

The scope of using the secret accounts across government remains a mystery: Most U.S. agencies have failed to turn over lists of political appointees' email addresses, which the AP sought under the Freedom of Information Act more than three months ago. The Labor Department initially asked the AP to pay more than $1 million for its email addresses.

The AP asked for the addresses following last year's disclosures that the former administrator of the Environmental Protection Agency had used separate email accounts at work. The practice is separate from officials who use personal, non-government email accounts for work, which generally is discouraged -- but often happens anyway -- due to laws requiring that most federal records be preserved.

The secret email accounts complicate an agency's legal responsibilities to find and turn over emails in response to congressional or internal investigations, civil lawsuits or public records requests because employees assigned to compile such responses would necessarily need to know about the accounts to search them. Secret accounts also drive perceptions that government officials are trying to hide actions or decisions.

"What happens when that person doesn't work there anymore? He leaves and someone makes a request (to review emails) in two years," said Kel McClanahan, executive director of National Security Counselors, an open government group. "Who's going to know to search the other accounts? You would hope that agencies doing this would keep a list of aliases in a desk drawer, but you know that isn't happening."