Bounce rate = bounced emails / emails sent x 100. A campaign sends 400 emails and 12 bounce: 12 / 400 x 100 = 3%.
A bounce comes back as a delivery status notification with a code. Codes starting with 5 are permanent, such as an address that does not exist; codes starting with 4 are temporary, such as a full mailbox. Most tools count both in the bounce rate, but they mean different things, so look at hard bounces and soft bounces separately.
Why bounce rate matters in cold email
Mailbox providers read a high bounce rate as a sign you did not collect your list carefully, which lowers your sender reputation. Cold lists bounce more than opt-in lists because people change jobs and companies change domains. Many senders aim to keep bounces under about 2%, and treat anything near 5% as a reason to stop and clean the list.
How to keep it low
- Verify every address before it enters a campaign, and treat catch-all and risky results with care.
- Refresh old lists; job changes turn valid addresses into bounces within months.
- Remove hard bounces at once and never retry them.
- Watch the rate per campaign, not only per account, so one bad list does not hide inside good ones.
In ZicReach, every campaign has a bounce limit, 5% by default, that pauses it on its own, and a rejected address is marked bounced in every campaign and suppressed without blaming the mailbox. Lists can be verified before sending, with each address marked Valid, Catch-all, Risky or Invalid in the AI Leads Engine. The AI Email Marketing page shows the campaign settings.