Bounce Rate

What is Bounce Rate?

Bounce rate is the percentage of emails in a given send that were rejected by the recipient's mail server and could not be delivered. It is a primary health signal for both list quality and sender reputation, and it is one of the first metrics mailbox providers look at when deciding where to route your mail.

Why it matters

A rising bounce rate is the canary in the deliverability coal mine. Anything above 2 percent for a marketing campaign is a warning, and above 5 percent many providers will start throttling or filtering you. Growth marketers, lifecycle managers, and anyone responsible for the sending program should watch bounce rate per campaign and per segment.

How it works

Bounce rate is calculated as bounced messages divided by accepted messages, usually expressed as a percentage. Bounces are classified as hard (permanent, like an unknown user) or soft (temporary, like a full mailbox). The sending platform parses the SMTP response or the DSN message and assigns a category. Good services remove hard bounces from your list automatically so you never retry them.

Examples

• A SaaS sending 50,000 emails per month with a 0.3 percent hard bounce rate
• A newsletter that sees bounce rate spike from 1 to 7 percent after importing an old list
• A transactional service maintaining under 0.1 percent bounces thanks to real-time validation at signup

Best practices

• Keep hard bounce rate under 2 percent for marketing sends
• Remove hard bounces from your active list immediately, never retry
• Use double opt-in to prevent typos from entering the list in the first place
• Let Sendkit categorize bounces automatically so you do not parse DSNs by hand

FAQs

What is the difference between a hard and soft bounce?

A hard bounce is permanent, usually caused by a nonexistent address or closed domain. A soft bounce is temporary, such as a full mailbox or a server outage, and the message may succeed on retry.

Does a high bounce rate hurt my sender reputation?

Yes. Mailbox providers interpret a high bounce rate as a sign you are not maintaining your list, which damages inbox placement for future sends.

Should I retry soft bounces?

Most providers retry automatically for a limited window, typically 24 to 72 hours. After that, treat the address like a hard bounce if it keeps failing.