Hello Everyone are facing a problem that we can't send any email to outlook, Hotmail, MSN, and Outlook.com all our emails are rejected. I contacted outlook.com team and they said that we are sending to many emails or namespace mining they gave me a a specific time and date when this happened, my problem is that we didn't recognize any unusual activity while checking the logs from the mail flow, any other idea how can we check if there is any malicious emails that has been send in this particular date using exchange management shell as per Outlook team it happened in the 10 of December.
Best regards