Hi,DSGraham In most email clients and systems (such as Microsoft Outlook/Exchange or Thunderbird), retention policy enforcement does not occur immediately when the limit is reached. The timing depends on the platform used: Microsoft Outlook / Exchange (Office 365) If you use Microsoft 365 work or school email, the policy is processed by a process called the Managed Folder Assistant (MFA). Frequency: In Exchange Online, this process runs automatically every 7 days. How to speed it up: Administrators can force this process for a specific mailbox using the Start-ManagedFolderAssistant PowerShell command. Mozilla Thunderbird In Thunderbird, message limits are configured in the folder properties on the "Retention Policy" tab. Frequency: Deletion typically occurs when the folder is opened or during the folder compaction process. Note: If a folder is inactive or automatic compaction is disabled, excess messages may remain in it longer than intended.