New York City Mayor Bill de Blasio (D) used a personal email account for official business hundreds of times, the city's Department of Investigation found.

The New York Times reported on Tuesday that an agency document acquired through a Freedom of Information Act request revealed that de Blasio and his closest aides used personal email accounts to discuss and conduct city business. The mayor used his for official purposes a total of 1,850 times, more than anyone else.

According to the Times, the mayor's use of a personal email account in some cases violated unofficial city guidelines on public official's use of email.

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The agency memo was part of an investigation into de Blasio's fundraising and whether he improperly helped a donor who was in a multimillion dollar lease dispute with the city.

The document also revealed the city official responsible for leases told investigators that the dispute with the donor marked "the first and only time that the mayor ever called her directly.”

In March, prosecutors announced that de Blasio wouldn't face criminal charges, but warned that they had investigated “several circumstances in which Mayor de Blasio and others acting on his behalf solicited donations from individuals who sought official favors from the city, after which the mayor made or directed inquiries to relevant city agencies on behalf of those donors.”

A spokesman for the mayor's office told The New York Times that the city had no official policy governing the use of personal email.

“D.O.I. is right,” a spokesman said in a statement. “Employees are supposed to use their government email for government work. That’s always been the protocol and we remind City Hall and agency staff of that frequently. We consider personal email and documents in someone’s personal possession subject to [the Freedom of Information Act] when they relate to government business,” he said.