Mayor Thomas M. Menino’s administration, prompted by public records requests from the Globe, has acknowledged that city employees were routinely deleting e-mails, a potential violation of the state public records law.

The acknowledgement came after the Globe filed several requests for e-mails sent and received by Menino’s Cabinet chief of policy and planning, Michael J. Kineavy. He is one of Menino’s most powerful and trusted advisers, intimately involved in nearly everything at City Hall, but a search of city computers found just 18 e-mails he had sent or received between Oct. 1, 2008, and March 31 of this year.

The unusually low figure prompted administration officials to question him about what happened to the rest of the e-mails he was presumably sending and receiving during that period. Kineavy, who is also one of the mayor’s chief political advisers and a strategist on Menino’s reelection campaigns since 1993, told them that he deletes all his e-mails on a daily basis, in such a way that they are not saved on city backup computers, administration officials said.

There are indications that Kineavy was not the only city employee who may have violated the law. In June, the Globe filed requests for copies of six months’ worth of e-mails sent or received by five other employees, including Transportation Commissioner Thomas Tinlin. City officials said that a search for Tinlin’s e-mails turned up only those he had received, none he had sent.

Alarmed by the deletion of e-mails that could have contained potentially significant information, administration officials recently instituted a new electronic document retention policy and temporary “journaling’’ program, to keep copies of every e-mail sent and received by every city employee.

The city’s chief lawyer, William Sinnott, said the city is working on a more permanent fix. Sinnott also said problems with preserving e-mail are not unique to Boston. “E-mail retention is a challenge with which cities and towns throughout the country struggle,’’ he said. “Both the law and the technology in this area have been evolving and the city has made every effort to comply with the law as we understand it.’’

According to the Massachusetts secretary of state, the state public records law requires municipal employees to save electronic correspondence for at least two years, even if the contents are of “no informational or evidential value.’’ The only e-mails that can be deleted are those containing completely inconsequential information, such as spam or questions about lunch orders.

“Clearly, employees cannot delete e-mails that have substantial content,’’ said Secretary of State William F. Galvin, who is responsible for enforcing the law. “The improper deletion of e-mail is a violation of the public records law. Period.’’

Without copies of substantive e-mails that Kineavy or others deleted, however, there is no proof of violations and therefore no sanctions can be imposed, Galvin’s office said. Violations can result in fines of up to $500 or prison sentences of up to a year.

The Globe obtained the e-mails of only two employees as a result of its requests, in part because of the cost estimates provided by the Menino administration. City officials estimated they would charge $5,000 for six months worth of e-mail for each employee, for a total cost of $30,000.

One City Hall watchdog said the Menino administration should have known better than to allow top officials to delete e-mails without keeping backup records. Samuel R. Tyler, president of the Boston Municipal Research Bureau, said Kineavy holds a critical position in the administration, where a lot of business that the public should be privy to is conducted.

“The city needs to institute a system to make sure those e-mails are protected and preserved,’’ Tyler said.

Pamela H. Wilmot, executive director of Common Cause of Massachusetts, a nonprofit group that focuses on government accountability, agreed.

“I wouldn’t be surprised if a top government official wouldn’t have 10,000 e-mails,’’ she said. “People write you from all sorts of quarters and, whether you send things back or not, incoming traffic needs to be retained.’’

The city’s most powerful official, Menino, leaves almost no electronic trail that is subject to the public records law, in part because he conducts some city business on his personal cellphone and does not use e-mail.

Stephanie Ebbert of the Globe staff contributed to this report. Donovan Slack can be reached at dslack@globe.com. Michael Levenson can be reached at mlevenson@globe.com.

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