The email provider notifies Sprwt about each message. Per sent email Sprwt stores a delivery status – processed, dropped, delivered, deferred, bounce or blocked (and canceled when a campaign is canceled) – and logs engagement events: open, click (with the URL and the recipient's mail client), spam report, unsubscribe, group unsubscribe and group resubscribe. These feed the campaign statistics (Opened, Clicked, Unsubscribed, Spam complaints, Bounced, Reading environment, Top email clients) and, for flow emails, the Email was opened / clicked conditions. Sprwt also drops a message before delivery for a recipient who has previously unsubscribed.