Office 365 Email Cleanup

My Office 365 tenant was compromised and spam is both being sent from and funneled into several mailboxes. I still have full access to every account and I have already changed all user passwords, but the unwanted messages keep coming, so the breach clearly runs deeper than simple credentials.

I need an experienced Microsoft 365 security specialist to:

• Trace and eliminate the source of the spam (malicious rules, forwarding, connected apps, or transport agents).
• Scrub every mailbox, quarantine suspicious items, and make sure no back-door forwarding or delegate permissions remain.
• Review audit logs and sign-in reports to confirm the attacker’s entry points and last activity.
• Reinforce the tenant with best-practice hardening: conditional access, two-factor authentication, Safe Links, Safe Attachments, and alert policies.
• Provide a brief post-mortem report that explains what happened, what was cleaned, and how to avoid a recurrence.

Acceptance will be based on the spam flow stopping for at least 48 hours, clean security scores in the Microsoft 365 Security Center, and the written remediation report.