When an email address is undeliverable due to a bounce, the entry is flagged in your account under the subscriber's profile. You can also view all bounces for the list from the "Undeliverable" filter on the " Subscribers " page.
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We will continue to send messages to a subscriber until they have been undeliverable three or more times in a 6-month period. To reduce false positive, we do wait at least 7 days from the 1st bounce recorded before unsubscribing. That means if a subscriber has bounced 3 or more times in that 6-month period, they will be unsubscribed on the next bounce after the 7 day window is concluded.
This process will reset every 6 months after a bounce is recorded. So, if a subscriber is undeliverable three times in a 7-day period and does not bounce for another 6 months, they will not be unsubscribed.
After the 6 month period has ended, this process resets and a subscriber will need to be undeliverable more than three times in a 6-month period to be unsubscribed.