You can control how your PoliteMail data is archived through the Settings >> Archiving tab.

PoliteMail will automatically compile interactions into final reports once the send date reaches the Archive age you set.
Individual interaction records will be permanently removed, but the metrics data will be preserved as a report. No drill down, follow-up or additional data collection will function for archived sends. Content downloads and tracked links will still function, but no data will be collected.

To enable archiving of messages, set the drop down to ‘Enabled’ and choose set your Archive age.