Some Catholic high school students in the Wollongong diocese are in hot water over emails containing "explicit language and offensive comments".
The emails were received by every Catholic high school student in the diocese.
Some of the emails, seen by the Mercury, include racist words and emojis used to spell out sexual acts.
The mass spamming occurred on Tuesday afternoon and parents were quickly notified.
On Tuesday night, the diocese's Director of Schools Peter Hill sent a letter to all parents about the spamming, which started with one student emailing a distribution group that included all secondary students at the diocese.
It is unclear how the student gained access to the schools' distribution list.
"A small number of students sent replies using the 'Reply All' function, some of which contained explicit language and offensive comments," Mr Hill said.
Once the Catholic Education Office was made aware of the emails, Mr Hill said the capacity for students to send emails to the distribution list was removed and all the emails deleted from students' inboxes.
"Catholic Education Diocese of Wollongong takes this matter very seriously," Mr Hill said the letter to parents.
"The behaviour of those students involved is unacceptable and does not reflect the values held by our schools. Schools will be taking appropriate action to sanction students involved in accordance with our student management procedures."
He also said counselling support has been offered to all students.