"It was premeditated, nasty and it was vicious," he said.
Kronfeld was sentenced to 120 hours' community work and the judge recommended it was done through an agency placement.
The court heard at trial how the affair with the married man - whose identity is suppressed - began shortly after their paths crossed at a conference in Auckland.
When they met again for another event in the city in January 2011 things got steamy.
From the witness box, Kronfeld spoke about how the man had kissed her in the middle of a Viaduct hotel foyer before inviting her to his room.
The secret trysts continued until they were twice spotted in public and colleagues of the defendant told her to "get it sorted".
"Best you stick to your home-made lunches," a friend of the man messaged him after seeing the couple out in Auckland having dinner one night.
In February 2014, Kronfeld issued an ultimatum, telling the man to choose between her and his wife.
When the man chose the latter, his wife started receiving frequent emails from a variety of anonymous accounts.
Kronfeld admitted being behind the flurry of abuse, but said it was to simply annoy the woman rather than cause her psychological harm or break up the marriage.
She confirmed she set up email addresses in a dozen different names including Chelsea Brown, Chelsea Sugar, D Milne, T Hopkins and Mee Wright.
Over the course of months she messaged the wife, calling her "spineless" and a "bitch", as well as repeatedly discussing the man's infidelity; telling her she was "married to a man with a hungry, wandering penis".
In early 2015, nearly a year after the affair had ended, the defendant also accessed the married couple's email account as well as their daughter's school database.
Judge Crosbie said the computer access was "voyeuristic" and the affect on the victim had been "profound".
"She did nothing . . . All she had done was remain loyal to her husband and family, perhaps it was that loyalty that incited the behaviour," the judge said.
In sentencing, he referenced the Jeremy Buis harassment case which came before the Dunedin District Court last week.
However, Judge Crosbie said that example was much more serious - "public harassment by a public servant".
He believed Kronfeld showed no remorse during the trial and hoped the time since then had allowed her to reflect on the episode.
No emotional harm reparation was ordered, but Kronfeld must pay court costs and witness expenses.
