GUILDERLAND — It’s a time of year that brings out not only holiday joy but also thieves. 

“The only way they had found out,” said Altamont’s postmaster, Bill Van Dyke, “is that a mail carrier had noticed four or five mailboxes on the route had had their flags up, but nothing inside the mailbox.”

The mail carrier was able to speak to one homeowner, Van Dyke said, who said he had put mail in the box earlier. 

Someone has apparently been stealing mail out of home mailboxes in Guilderland and Altamont. Areas with reports of incidents are Westmere, Whipple Way in the village of Altamont, and the Twenty West neighborhood in western Guilderland. 

“I believe it’s outgoing mail,” said Van Dyke. Someone else, he said, was contacted the next day by a bank who informed them that a check of theirs had been altered. 

“If I understand it right, they’re altering the checks and then trying to cash them,” Van Dyke explained. 

During the holiday season, the postmaster said, “There’s always a rise in people stealing packages off stoops or trying to get something for nothing, trying to get the best of somebody.” 

In late November, a package thief was caught on a home surveillance camera stealing a box from a front porch in Windmill Estates. In that case, the package was returned after video of the incident was shared widely, and the homeowner declined to press charges. 

Van Dyke said he knew of incidents in the Twenty West area and on Whipple Way in Altamont. 

He is advising people who believe that their mail may have been stolen to contact the local police as well as the United States Postal Inspection Service — the law-enforcement arm of the United States Postal Service, which investigates criminal matters involving the integrity and security of the mail. 

Deputy Chief Curtis Cox of the Guilderland Police said that investigators are working with U.S. Postal Inspectors on the case. 

“I guess the best thing might be to bring the mail here” rather than leaving it in the mailbox with the flag up,” said Van Dyke at the Altamont Post Office this week. 

But, he said, referring to the thief or thieves, “I don’t like to make people feel like they’re winning.”