Email bounce rate is the percentage of emails that do not reach the recipient. You can calculate it by dividing the number of bounced emails by the total sent. You should aim for a low bounce rate to improve email deliverability. A high bounce rate can indicate problems with your email list such as invalid or outdated addresses. You can reduce bounce rates by cleaning your list regularly. You must verify email addresses before sending messages. You should also avoid using spammy content that might cause your emails to be blocked. A good bounce rate is under 2%.