Anwar Akhtar, 40, first met the victim while he was working on November 6, 2018.
Akhtar then approached her twice while she was shopping in Queensgate and made inappropriate comments.
Soon after the victim started to receive letters at her place of work, causing her to report him to the police.
Akhtar was visited by officers on January 2 last year and was spoken to. Following this involvement contact ceased for a few months.
However, the letters began again, initially written as love letters but quickly developing into being threatening and abusive in nature.
One letter said “I’m gunna smash your face in” and another contained her car registration plate.
The letters caused her so much distress that she changed jobs, moved house and replaced her car.
She reported the incidents to the police and Akhtar was arrested on 12 January this year.
Akhtar, of Cromwell Road, admitted charges of harassment, stalking and making threats to kill.
He was sentenced yesterday, August 12, at Peterborough Crown Court to three years in prison and handed an indefinite restraining order.
DC Jenny Blunt said: “Akhtar was clearly intent on contacting the victim despite her never once responding to his messages.
“He caused her extreme distress and I hope this shows how seriously we take incidents of harassment.
“Justice has been served and an indefinite restraining order has been put in place.”