What is bounce rate?
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You send 10,000 emails. A few hundred come back rejected. That rejection rate is your bounce rate, and it's one of the clearest signals of your list health.
Bounce rate is the percentage of emails that couldn't be delivered and were returned by the receiving server. Each failed delivery includes an SMTP status code explaining why: 550 means the address doesn't exist, 421 means the server was temporarily unavailable, and so on. Your ESP translates these codes into "hard bounce" (permanent failure) or "soft bounce" (temporary failure) and records them in your campaign report.
It's one of the most watched metrics in email because mailbox providers use it to judge whether you're a responsible sender. A high bounce rate signals that you're mailing to bad data, which is a red flag for spam filters. If your rate climbs above 2%, expect your deliverability to suffer. Above 5%, you're in serious trouble and your ESP may suspend your account.
Bounce rate is calculated simply: bounces divided by emails sent, multiplied by 100. So 200 bounces from 10,000 sends is a 2% bounce rate. Keep your total bounce rate below 2%, and your hard bounce rate below 0.5%. If you're above those thresholds, list cleaning and suppression should be your first move. Review My Emails can clean your list before your next send if you'd rather not guess which addresses are causing the problem.
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