In Microsoft Exchange Online for Microsoft Office 365, you apply a retention policy that moves email messages from a user’s mailbox to the archive mailbox. In this scenario, the retention policy does not automatically run.
The issue occurs because the retention policy runs automatically one time every 7 days for mailboxes that are larger than 10 MB. However, the retention policy does not automatically run for mailboxes that are smaller than 10 MB or within 7 days’ work cycle.
To resolve the issue, manually run Start-ManagedFolderAssistant –Identity <mailbox> cmdlet to force Managed Folder Assistant to process the specific mailbox in Exchange Online for Office 365.
//To resolve the issue, follow the steps:
1. Connect Windows PowerShell to cloud-based service.
2. Manually run Start-ManagedFolderAssistant –Identity <mailbox> cmdlet to force Managed Folder Assistant to process the specific mailbox.
Messages are not automatically moved to a user's archive mailbox after you create a retention policy in Exchange Online for Office 365
Set Up and Manage Retention Policies in Exchange Online
Connect Windows PowerShell to the Service
Office 365 Exchange Online