A cloud-based service included in Microsoft 365, delivering scalable messaging and collaboration features with simplified management and automatic updates.
You will need to search the Audit Log for any the following operation: New-MailContact
Connect to Compliance and Security powershell module: https://learn.microsoft.com/en-us/powershell/exchange/connect-to-scc-powershell?view=exchange-ps
Verify if the audit log is enabled for your tenant: Get-AdminAuditLogConfig | FL UnifiedAuditLogIngestionEnabled
Make sure you have the required permissions: You have to be assigned the View-Only Audit Logs or Audit Logs role in Exchange Online to search the audit log. By default, these roles are assigned to the Compliance Management and Organization Management role groups on the Permissions page in the Exchange admin center.
Use the following command: https://learn.microsoft.com/en-us/powershell/module/exchange/search-unifiedauditlog?view=exchange-ps
Example: Search-UnifiedAuditLog -Operations New-MailContact
NOTE: audit log are subject to retention policies defined by default by Microsoft, 1 year for E5 users and 90 days for non-E5 users.
Details: https://learn.microsoft.com/en-us/microsoft-365/compliance/search-the-audit-log-in-security-and-compliance?view=o365-worldwide