A bounce is an email that could not be delivered.
- Hard bounce: the address does not exist or the receiving server rejected the email. The person is stopped in the sequence, added to Blocked addresses, and never gets email from your workspace again.
- Soft bounce: a full mailbox, a server temporarily not answering and so on. The address is not blocked.
The bounce rate directly affects your sending reputation. If a campaign's bounce rate goes above 5% over the last 24 hours, the campaign pauses automatically and waits until you check and resume it. The domain's daily limit is lowered when the rate rises, too.
To keep the rate low, prefer addresses marked Verified in the results table and don't add old addresses or ones from other sources to a campaign.