Definitions
The delivery of some emails and SMS may fail and return an error commonly called "bounce". These errors are classified into two categories:
SOFT bounce, meaning a temporary issue.
HARD bounce, meaning a permanent delivery problem.
To understand the difference between soft and hard bounces depending on the canal you are using, you can read the following table.
SOFT bounces | HARD bounces | |
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Emails |
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SMS |
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Calculating bounce rates
The performance evaluation of the targeting and the sending can be done based on the SOFT and HARD bounce rates. The bounce rates are calculated using the following formula:
SOFT bounce rate = number of SOFT bounce emails / number of emails sent
HARD bounce rate = number of HARD bounce emails / number of emails sent
Understanding bounce recovery (emails only)
Almost all soft or hard bounces are obtained synchronously, which means during the SMTP transaction the email server returns directly a confirmation or an error if the recipient exists or if the message has been accepted or not.
However some bounces are recovered asynchronously, in this case, they are obtained through the return address set for sending. In rare cases, these returns can be sent and thus recovered several hours or even several days after sending the message.