outlook group email became a FB discussion

Sent out a group email through outlook on the web (msn) to people with fb email addresses. The email became a discussion that won't stop. Everyone on the list is getting everyone elses emails stating they are leaving the conversation but no one is leaving because everyone keeps sending the same message "I am leaving the conversation". The email was never meant to be a conversation it was  a one time email. period how do we stop it!!   I don't know if its the mobile version? It is on my MSN account as my email.