What does AWeber do with undeliverable subscribers?

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.

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.