Magistrates in Boston had ordered the destruction of 'Pru' - an eight-year-old Alsatian- after she nipped long serving postie, David Reeson.
But Pru's devoted owner, Lorraine Nassau, launched a legal fight to save her beloved dog from being 'put down' after calling the decision "callous."
And a judge agreed to spare Pru after Mrs Nassau appeared at Lincoln Crown Court.
Mrs Nassau, 55, of Sea End Road, Benington near Boston, had admitted being the owner of a dangerous dog when she appeared before Magistrates in December.
But she insisted Pru is a "very loving dog" who was only doing her job by protecting the family who rescued her two years ago.
The appeal hearing was told Mr Reeson, a postman of 20 years service, went to Mrs Nassau's home to deliver a package on August 10.
Mrs Nassau told the appeal hearing: "Pru has been absolutely fine since she came to us but she was a shivering mess when we rescued her
“I think she had been used as a breeding bitch. She had not been socialised. We took her because she was going to be put to sleep.
"We’ve got three-quarters of an acre of land so there’s plenty room for her to run around.
“We have a box fitted to the gate so our regular postman would put the post there. On this day it was a relief postman and I don’t think he knew the procedure."
She told the court that since the incident the front gate has been padlocked.
“Nobody can get in the gate any more. It’s padlocked with a chain. We’ve put new signs up. They say “Do not enter. Dogs roaming free”.
Mrs Nassau said that Pru does not normally show aggressive behaviour towards people or towards other dogs.
Tony Stanford, for the Crown, told the appeal hearing “On this day a postman was delivering mail to the house. The front door of the home was shut.
“The two dogs ran out and Mr Reeson turned his back on them. One of the dogs, Pru, bit him to the back of his right leg. Mrs Nassau came out and immediately assisted with first aid for the postman."
Recorder William Harbage QC, sitting with two magistrates, suspended the order that Pru should be put down and replaced it with a conditional destruction order.
He imposed a series of conditions which mean that Pru must be on a lead at all times in public; Pru and her owners have to undertake a training course within the next six months; the front gate to Lorraine’s property has to be secured with a chain and padlock; and warning signs have to be placed at the gate with a telephone number for callers to ring before entering.
Magistrates had previously ordered Mrs Nassau to pay compensation of £500 to the postman and ordered destruction of the dog within 28 days. She was also ordered to pay £85 in court costs.
Recorder Harbage said “We have considered all matters and we don’t find a destruction order is warranted. We have no hesitation in saying that Mrs Nassau is a fit and proper person to be in charge of the dog. She is clearly passionate about the dog.”