When Mr Chan's boss Mark Satherley pulled him up on the rude email, he hit back saying he was being bullied and intimidated, and branded the customer 'Miss Piggy'.
"After your repeated threats to dismiss me I believed that I no longer had my job, so in response to viewing Miss Piggy's complaint which you posted to me, I replied to her directly," Mr Chan said.
In a later disciplinary meeting Mr Chan said the customer had no right to make a complaint, and she was "stirring things up and there is such a thing as free speech".
But the Employment Relations Authority ruled that Mr Chan was not being bullied by his bosses, and was not unfairly dismissed.
"... he expressed no remorse for [the email]. He attempted to put the blame for his conduct on his employer and on the customer herself for having complained about his behaviour towards her in the first instance," the ERA said in its decision.
"Mr Chan's email on its own may have justified dismissal. Coupled with his failure to acknowledge any culpability for his action, and his blaming of everyone but himself for it, I have no hesitation in finding his employer was justified in dismissing him."