The Postal Service is replacing 49,000 so-called arrow locks with electronic versions to make them less attractive to criminals who have been targeting them to steal mail from secure receptacles, and it is placing 12,000 hardened blue collection boxes in high-risk areas, according to the Postal Service and Postal Inspection Service.

The announcement came days after the National Association of Letter Carriers expressed outrage as The Associated Press reported that nearly 500 postal carriers were robbed last year.

“We’re doubling down on our efforts to protect our postal employees and the security of the mail. We are hardening targets — both physical and digital — to make them less desirable to thieves and working with our law enforcement partners to bring perpetrators to justice,” Postal Inspection Service Chief Gary Barksdale said Friday in a statement.

The spike in postal carrier robberies has put letter carriers on edge.

The robberies have more than quadrupled over a decade, and weapons were used in most of the 496 robberies last year, according to data provided by the Postal Inspection Service to the AP under the Freedom of Information Act. Thirty-one postal carriers were injured, and one of them was killed last year, according to the data.

On Thursday, federal officials announced two more people were charged on allegations of pulling a letter carrier off a home’s front steps while stealing an arrow key and using a knife to rob another carrier last year in Massachusetts.

The Postal Service declined to say how many arrow keys are in use with the nation’s nearly 250,000 letter carriers.

But efforts by criminals to intercept the mail go beyond robberies to steal those keys. The Postal Service said also there were 38,500 thefts of mail from blue collection boxes in the 2022 fiscal year.

Criminals are targeting the mail, often in an organized fashion, to commit financial crimes, including altering checks to commit check fraud, officials said, but there are steep federal penalties for doing so.

Postmaster General Louis DeJoy said the carriers who deliver 162.1 million pieces of first-class mail each day should be able to work “in safety and to be free from targeting by criminals seeking to access the public’s mail.”

Mail theft carries a penalty of up to five years in prison. Possession, concealment or disposal of property carries a sentence of as many as 10 years in prison. Assault carries a sentence of up to 10 years for a first offense, and up to 25 years for any subsequent offense, officials said. Federal prosecutors can also bring other charges, as well.

Postal officials are cracking down on other ways criminals are targeting the service.

The service began implementing dual authentication for identity verification online for changes in address last month, and is starting enhanced in-person change-of-address transactions by month’s end to prevent criminals from using change-of-address protocols for identity theft to intercept credit cards, checks and other financial mail. The Postal Service is no longer accepting third-party change-of-address submissions.

The service is also tackling counterfeit postage. It will exercise new authority to take possession and dispose of packages with counterfeit postage and to shut down websites selling counterfeit postage, officials said.

Postal officials seized more than 340,000 packages with counterfeit postage and more than 7.7 million counterfeit stamps, preventing the loss of an estimated $7.8 million in postal revenue, in the last fiscal year, officials said.