Royal Mail said it was investigating a spate of post box thefts in the Peterborough area.
The latest went missing from the village of Holme last week.
However, the company said while the theft of post boxes was "relatively rare", it was aware of "several" in the area and was working with police to prevent their removal.
Cambridgeshire Police confirmed it was investigating the Holme theft and the force appealed for witnesses.
The theft of the small box, mounted on a steel pole, took place on Church Street in the village between 12:55 GMT on 16 November and 14:00 on 17 November, a spokesman said.
Holme parish councillor Janice Osborn said: "It was there on Monday... when the vicar put a whole lot of letters in it, but on Tuesday... it wasn't there.
"It must be a two-man job, I think, to move a post box that size."
She said villagers were "stunned and shocked" by the theft.
"It is inconvenient - but it's not the end of the world," said Ms Osborn, who hoped the post box would be returned.
There is one other post box at the other end of the village, she added.
Royal Mail, which has about 115,000 post boxes across the UK, said it took the issue of their theft "very seriously" and was "working hard to replace the missing boxes".