A bounce is an error message that is automatically generated by the recipient server when an e-mail cannot be delivered. There is a difference between a hard bounce and a soft bounce.
The hard bounce is a permanent problem, e.g. that the address no longer exists. Addresses that generate a hard bounce are immediately unsubscribed by promio.connect and are not contacted again.
By contrast, a soft bounce is a temporary problem, e.g. a recipient’s absence during vacation or a full mailbox. The soft bounce rate is also an indicator of the address quality.
Bounces are marked in the data field “mailerror”:
0: delivered
1: hard bounce
2: soft bounce
3: quarantine