This story was co-published with the Albany Times-Union and WNYC.

New York Gov. Andrew M. Cuomo’s administration—which the governor pledged would be the most transparent in state history—has quietly adopted policies that allow it to purge the emails of tens of thousands of state employees, cutting off a key avenue for understanding and investigating state government.

Last year, the state started deleting any emails more than 90 days old that users hadn’t specifically saved—a much more aggressive stance than many other states. The policy shift was first reported by the Albany Times Union.

A previously unpublished memo outlining the policy raises new questions about the state’s stated rationale for its deletions policy. What’s more, the rules on which emails must be retained are bewilderingly complex—they fill 118 pages—leading to further concern that emails may not be saved at all.

“If you’re aggressively destroying your email, it looks like you’re trying to hide something,” said Benjamin Wright, a Dallas lawyer who has advised companies and government agencies on records retention.

ProPublica obtained the memo through a public records request.

In the June 18, 2013, memo, Karen Geduldig, the general counsel of the state’s Office of Information Technology Services, described New York’s decision to automatically delete emails as a way to cut down on the state’s “enormous amount of email data.”

But the state implemented the policy as part of a move to Microsoft’s Office 365 email system, which offers 50 gigabytes of space per email user—enough to store hundreds of thousands or even millions of emails for each state worker. The state’s version of Office 365 also offers unlimited email archiving.

The Office of Information and Technology Services declined to comment on the record. An official in the office said even though the state can store large quantities of email, it can still be difficult to manage.

“Just because you have a big house doesn’t mean you have to shove stuff in it,” the official said.

Geduldig’s memo also pointed out that some federal government agencies and corporations automatically purge employees’ email. “Such a system will aid the State in improving its email management,” Geduldig wrote.

But many states take a different tack.

Florida, for instance, requires state employees to keep routine administrative correspondence for at least three years, and emails dealing with policy development for at least five years. Connecticut requires employees to keep routine emails for at least two years. Washington State requires workers to keep emails dealing with public business for two years, and emails to and from top officials for four years. Those states also do not automatically delete email.

“It shouldn’t be an automatic process,” said Russell Wood, the records manager for the Washington State Archives. “There should be some point of review in there.”

Emails that qualify as “records” are supposed to be preserved under New York’s policy. But determining which emails qualify and which don’t—a task left up to individual state employees—can be mind-numbingly complicated.

The state’s rules include 215 different categories of records—including two separate categories dealing with office supplies.

“We don’t think it’s plausible at all that agency personnel are going to meticulously follow” those rules, said John Kaehny, the executive director of the good-government group Reinvent Albany. If the rules for preservation aren’t followed, emails will be purged by default.

The length of time emails are required to be kept varies by category. Any emails related to “human rights training,” for instance, must be kept for six years. Emails concerning “agency fiscal management” must be kept for three years. Emails about “the development of internal administrative policies and procedures” must be kept for a year, but emails “used to support administrative analysis, planning and development of procedures” can be deleted as soon as they’re “obsolete,” according to the rules.

The governor’s office has its own rules detailing which emails must be saved, with 55 categories, from emails of weekly reports to emails “related to Native-American affairs.” Anything that doesn’t fall into one of the categories “should be deleted” once they’ve been opened, the governor’s office advises.

There is no internal or external watchdog to make sure the rules are being followed, Kaehny said.

The state also doesn’t have a standardized system for preserving emails that do have to be saved, according to the Office of Information Technology Services official. State workers can save their emails by printing them out, pasting them into Microsoft Word documents or placing them in a special folder in the email program itself.

“Everyone does it differently, and some people are still learning how to do it,” the official said.

Emails related to potential litigation and freedom of information requests are not supposed to be deleted under New York State’s policy. But Karl Olson, a San Francisco lawyer who has represented news outlets including the Los Angeles Times in freedom of information lawsuits, said that deleting emails after such a short period of time might mean they’re gone by the time reporters need to request them.

“It may take a while for evidence of misconduct to bubble to the surface,” Olson said.

Emily Grannis, a fellow with the nonprofit Reporters Committee for Freedom of the Press, said New York’s automatic deletion policy “strikes me as inconsistent with the goals of [freedom of information] laws, and to have such a short timeframe is particularly troubling.”

Government agencies often adopt deletion policies to help protect themselves from potential lawsuits and freedom of information requests, said Mark Diamond, the chief executive of Contoural, a records management consulting firm. Getting rid of emails after 90 days, though, risks deleting correspondence that employees might need down the road. “I don’t think it’s a well thought-out strategy,” he said.

Cuomo’s aides have also developed a reputation for using their personal email accounts to conduct state business—a move that can make it more difficult to seek the emails under the state’s freedom of information law. The Cuomo administration has denied that it does so, but a ProPublica reporter and others have, in fact, received such emails from officials.

New York isn’t the only state that destroys unsaved email after 90 days.

California’s governor’s office, for instance, has automatically deleted employees’ sent and received email after 90 days for more than a decade. But the office also requires employees to save far more than in New York, including official correspondence, memos, scheduling requests and other documents.

If you have information about or experience with the state’s email deletion policy, please contact Theo Meyer at theo.meyer@propublica.org.

Related articles: Read our coverage of how Cuomo administration officials have used their private email accounts for public business, and how the administration has denied that it does so.

Justin Elliott contributed reporting.