Once the user has archive enabled, and assigned to the archiveDatabase, you need to make sure it's configured for MRM as you've stated. The archiving is then processed by the Managed Folder Assistant which should process all mailboxes on a mailbox server within a one day by default. (I hope you are seeing some result by today since your initial post was 18hrs ago)
You can verify the Managed Folder Assistance by checking the ManagedFolderWorkCycle attribute for your mailboxserverGet-MailboxServer | Format-Table name,ManagedFolderWorkCycle* -Auto
You can also trigger it for the user by PS
Start-ManagedFolderAssistant -Identity username@domain.com
You can find more information about Configuring Managed Folder Assistant and Messaging Records Management Procedures here
Configure the Managed Folder Assistant