A Sydney father has been ordered to pay more than $80,000 for defaming a school principal in a string of emails.

Beecroft Primary School Principal Jenny Ryan sued Rajaratnam Premachandran over an email he sent to her and other parents at the school after his daughter performed poorly in a selective school's test.

The email described Mrs Ryan as incompetent and untrustworthy and called for her to quit.

He also made complaints that she was racist and possibly abusive.

Mrs Ryan said Mr Premachandran ran a malicious campaign against her for a year.

In the Supreme Court today, Justice Henric Nicholas ruled in favour of Mrs Ryan and ordered Mr Premachandran to pay more than $80,000 in damages.

The judge ruled that the rumours significantly damaged Mrs Ryan's reputation and caused distress that continues to this day.

Justice Henric Nicholas said Mr Premachandran was malicious for persistently defending himself without evidence.

The principal will apply to have him pay her legal costs.