Royal Mail wrote to the owners of four-year-old Bella to warn that unless she could be restrained, it would no longer deliver mail through the letterbox.
"Your postman has reported that when he pushes the mail through your letterbox your cat snatches the mail and puts his fingers at risk of injury," the letter said, according to The Times newspaper.
Owner Laura Lowe, a mother of two children who lives near Bristol in southwest England, said she initially found it hard to believe that her "lazy" black and white cat could be attacking postmen.
"Bella doesn't realise she's doing anything wrong, she thinks it's a game when she tries to grab things that come through the letterbox."
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A spokesman for Royal Mail told AFP: "We have now spoken to Bella's owners who have agreed to install an external mailbox that will allow the postman to deliver safely to the property."
Attacks by animals are a regular occurrence for postal staff and in recent years the Royal Mail has developed "posting pegs", strips of plastic that allow them to push letters through a door while keeping their hands clear.