One message from Ms Mutu to the student said: "Oh hang on, look at all the options then u make up ur own mind - u need to start carrying condoms with u too". The conversations were often late at night and initiated by the principal.
The tribunal's decision outlined that, on reflection, Ms Mutu said knew she had stepped over the line and "even when I was typing I knew it was wrong".
Ms Mutu said she had taken off her "professional hat" and put on her "aunty hat".
The tribunal's decision also found Ms Mutu showed favouritism toward some students and disclosed personal information about herself on Facebook to students. The former principal also allowed some students, whom she had known for a number of years, to stay overnight at her house as they lived far from the school. Ms Mutu lived alone.
The controversy around Ms Mutu's departure has been the catalyst for much conflict at the Maori immersion school, which saw its roll half at the start of this year.
Former chairman of the board Terry Smith said he was "relieved" the decision was out in the open as it exonerated the board's decision to fire Ms Mutu.
"For me it's just inappropriate," he said. "It's just unprofessional."
Mr Smith said many parents who supported Ms Mutu turned against the board which eventually led to questions about the validity of the board of trustee elections.
In June, the Ministry of Education dissolved the board of trustees and appointed commissioner Larry Forbes, though the board is going to court over the decision next month.
Mr Forbes said a new board was expected to be appointed in the first half of next year at which point his role would finish.
One of the parents who left the school, Gary Brambley, said real reason for the exodus of families at the start of the year was around students' physical safety, bullying of staff by board members, lack of a formal election process and lack of accountability.
Ms Mutu consented to her registration being cancelled as she did not wish to teach again and was ordered to pay $2000 toward the school's legal costs.