A bounce occurs when a sent message is rejected by the receiving mail server. The most common causes for bounced email messages include a misspelled or nonexistent email address. A repeat bounce is when an address has bounced, then bounced a second time and logged to the bounce suppression list, but you ask us to send to this recipient again. Our system will suppress the message because it 'knows' that recipient address is bad.
If you would like to receive a notification for each bounce message, you can turn on Bounce Forwarding in your Mail Settings.
In the top right corner, you will see a calendar icon. Click this and choose the dates you would like to search between. Your recipient list will refresh, showing the recipients who bounced between these dates.
You can download your Bounce list as a CSV by clicking the gear icon at the top of the page and selecting Download CSV. The file will download in your browser right away.
When you select the checkboxes next to the recipient names or select all, using the checkbox next to the search box, you will see a new button at the top of the page. From this list, you can choose to remove the selected recipients from the list. You can also use the Bounce Purge.
An asynchronous bounce, also known as an "out-of-band" bounce or "non-conversational" bounce, occurs when a message is initially accepted for delivery, but reported as a bounce at a later time. A message that results in an asynchronous bounce event should be considered undeliverable, despite the initial delivery event. In these instances, a single message may have both a delivery and a bounce event tied to it, and could result in apparent anomalies in your campaign statistics.
With an asynchronous bounce, a Delivery Status Notification (DSN) or Non-Delivery Report (NDR) is sent back to the email address that delivered the original message, providing detail as to why the message was undeliverable. These responses may be received minutes or hours after the message was initially accepted.
This behavior is unlike a synchronous, or "conversational" bounce, where the failure is recorded when the message is transmitted. With synchronous bounces, the remote mail server rejects the message outright, during the initial delivery attempt, and also will usually provide bounce codes indicating the reason for the rejection. A delivery event does not occur with a synchronous bounce.
Additionally, there is less contextual detail that can be tied to the event when asynchronous bounces take place, and as such the message ID data will not be available, and IP may not be available as well.
The vast majority of bounces are synchronous; asynchronous bounces are more commonly seen with corporate or small business domains, and thus may occur more frequently for B2B senders. Most major mailbox providers will generate only synchronous bounces.
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