NEW YORK (CBSNewYork) — A city document indicated that Mayor Bill de Blasio and four of his aides used personal email accounts for city business, sources said late Tuesday.

Sources told CBS2 Political Reporter Marcia Kramer about the use of the personal email accounts, which the New York Times also reported on Tuesday night.

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The Department of Investigation discovered the use of the accounts while investigating the mayor’s campaign fundraising lastyear, sources said.

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De Blasio was not charged criminally in connection with the campaign fundraising but, the U.S. Attorney’s office said the mayor intervened on behalf of donors seeking political favors, and the Manhattan District Attorney’s office said the way the mayor raised money violated the “spirit” of the law.

The mayor used his personal email address at least 1,850 times for conducting city business, sources said. The actions could be in violation of some city guidelines, sources said.

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CBS2 reached out to Mayor’s office spokesman Eric Phillips said in response to the reports: “We don’t recommend people use personal email. People rarely use personal email. We’ve stopped the limited practice of personal email.”