Cold email glossary
Bounce rate
Bounce rate is the percentage of sent emails that are rejected and returned undelivered by the receiving server. It is calculated by dividing bounced messages by total messages sent, and it is a primary signal of list quality.
What is bounce rate?
Bounces come in two kinds. A hard bounce is a permanent failure: the mailbox does not exist, the domain is invalid, or the receiving server refuses the sender outright. A soft bounce is temporary: the mailbox is full, the server is briefly unavailable, the message is too large, or the server is greylisting and asking the sender to retry. Hard bounces should be removed from a list immediately, and an address that soft bounces repeatedly is usually treated as a hard bounce.
Mailbox providers care about bounce rate because a high hard bounce rate is the signature of a scraped or stale list. Senders mailing well-maintained, verified lists rarely hit dead addresses, so a spike in bounces tells the receiving side a lot about how the list was sourced. The signal feeds into sender reputation, and many sending platforms pause campaigns on their own when bounces climb past a few percent.
Two measurement notes. Bounce rate in email is unrelated to website bounce rate, which measures visitors leaving a page. And a low bounce rate does not prove inbox placement: a server can accept a message and still route it to spam, which never shows up as a bounce. Bounce rate tells you about list quality, not about where accepted mail lands.
Why it matters in cold email
In cold email, bounce rate is the earliest and clearest health signal a campaign gives you. Practitioners typically keep it under 2 to 3 percent, and a sudden rise almost always means a list problem: unverified addresses, stale data, or too many catch-all domains. Continuing to send into a bounce spike compounds the damage, because reputation follows the sending domain, and a domain that providers learn to distrust gets worse placement on everything it sends afterward.
How Sendful handles it
Sendful verifies lists before launch and tracks bounce rates per campaign and per dedicated sending domain as part of weekly reporting. When a bounce rate moves, volume comes down and the list is rechecked before sending resumes. Your primary domain is never part of the equation, because Sendful never sends outreach from it.
What is a good bounce rate for cold email?
Practitioners typically aim to keep bounces under 2 to 3 percent. Sustained rates above that usually mean the list was never verified or has gone stale, and the sensible move is to pause, re-verify the list, and remove everything questionable before sending again.
What is the difference between a hard bounce and a soft bounce?
A hard bounce is permanent: the address or domain does not exist, or the server refuses the mail outright. A soft bounce is temporary: a full mailbox, a server hiccup, or greylisting. Hard bounces come off the list immediately; soft bounces can be retried, but repeated soft bounces should be treated as hard.
How do I reduce my email bounce rate?
Verify every address before sending, and re-verify older lists before reusing them. Remove hard bounces the moment they happen, limit how many catch-all addresses you mail, and make sure SPF, DKIM, and DMARC are configured correctly, since authentication failures can cause rejections even on valid addresses.
Book a call
Done reading? We run all of this for you.
Book a call and leave with a custom outbound plan, your ICP, opening sequences, and a deliverability check, whether or not we work together.