Two out of the three candidates withdrew their applications after receiving the letter, which raised questions about the resignations of the school's head and deputy.
Michael White, who taught at Park View school in Birmingham for 22 years and who had been its head of maths, handed out the letters when the candidates visited the school, which had been in special measures.
He was sacked in December 2003 after being found guilty of gross misconduct. Mr White said he was forced to sell his home and has since set up an electrical firm.
He denied his actions amounted to unacceptable professional conduct and told England's General Teaching Council this week that he had simply wanted to tell candidates about the school.
Mr White said that he had taken up the head's invitation for staff to meet the candidates and to give them a full and balanced view of the school.
"My actions were inadvisable in hindsight bearing in mind the repercussions but there was nothing in the letter that was untrue," he said.
"They were private letters to three professionals which helped paint a full picture of the school. When teachers are appointed to a position of deputy head it is vital they know the good and the not-so-good points.
"As a senior member of staff I had a duty of care beyond that of normal classroom teachers and I felt it my duty to share information with fellow professionals."
Mr White said he had helped turn the school around but that he was disappointed not to be appointed to a leadership role by the new head. He complained to the local authority and was unhappy with its response.
Mr White's application to become deputy head was also unsuccessful.
"I was not a happy man and I am still not because of the way I was treated but that was not the reason I sent the letter."
Lindsey Clark, head, said she felt as though she had been kicked when she read the letter and that it had a similar effect upon other staff. "I felt I could no longer have trust in Mr White as a senior member of staff.
"The school had a bad history but people had moved on and were beginning a fresh start as it had overcome its serious weaknesses. I considered Mr White was out to scupper the appointment of deputy headteacher."
The GTC decided not to impose a sanction on Mr White despite its ruling that he was guilty of unacceptable professional conduct.
Liz Paver, committee chair, said it had taken into account his long-standing career, the fact that no pupils were put at risk and that his family had already paid a high price.