Abdul Musa blew the whistle on problems at the Canterbury Street sorting office where he worked in Blackburn, Lancashire between 2006 and 2007.
Yesterday an employment tribunal ruled that Musa was racially victimised by his colleagues and the judge blasted Royal Mail's investigation into his slurs as "shambolic", the Daily Mail reported.
The tribunal judge ruled that Musa had been unfairly dismissed in July 2007 and upheld his racial discrimination claims.
The findings of a five-day tribunal, held in Manchester in January 2012, have only now been made public.
The Equality Commission attacked Royal Mail for failing to protect Musa, from Burnley, following efforts by a union and fellow staff to drive him out.
Asian workers, including Musa, were labelled "cockroaches" "vermin" and "P***s", the employment tribunal heard, and an Italian worker also received racial slurs and was dubbed a "greasy b******".
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But following Musa's complaints he was accused of a string of "quite incredible" racial and sexual counter-accusations, and sacked in early 2007.
Postal worker Christopher Eccles was also sacked, as a result of the ongoing abuse, and 12 colleagues were later disciplined.
The episode prompted strike action at the delivery office and the graffiti "Kill The P****" appeared in a staff toilet, the tribunal was told.
In a statement the Commission said: "The tribunal found that managers at the depot in Blackburn had known endemic racism was an issue, but failed to act to protect Mr Musa."
Tribunal judge Mrs C Porter said it was "quite startling" that the graffiti's origins were then never investigated.
"The procedure adopted by the respondent (Royal Mail) for the investigations and disciplinary action was shambolic," she said.
The former postman accused Royal Mail of failing to support him, after he made his original complaint, and breaching his confidentiality.
He said details of his claims were handed around the sorting office for others to read, leading to further intimidation.
The Equality and Human Rights Commission funded Musa's case after his previous legal representation withdrew from the proceedings.
A Royal Mail spokesman said: "There is no room in Royal Mail for racism or any other form of discrimination. We are committed to investigating any complaint of discrimination fairly and thoroughly."