There are two reasons this could be happening:
1. When an email is sent Swiftpage attempts to get it to the recipient once every eleven seconds. If it bounces back each time (we try three times), our system registers it as a Bounce. It is possible for an email to not get through on the first or second time but still get through. This could cause you to get undeliverable messages (from the first two bounces) even though the message still may have gotten to the recipient.
2. When our servers send an email, the server connects with the recipient's server to decide if it is deliverable. If the recipient's server initially accepts the email but later rejects it after the connection to the Swiftpage server has been lost, you may receive undeliverable messages in your inbox that will not appear on the bounce report online.
Note: Online reports will reflect an hourly update. Within integrations the information will be updated daily.