How does an email bounce work?
Every message is handed to the receiving server over SMTP. If the server rejects it, the sender gets back a status code and, usually, a delivery status notification — the bounce. Codes in the 5xx range mean a permanent failure; 4xx codes mean a temporary one. Your sending platform records the bounce, classifies it, and decides whether to retry.
What is the difference between a hard bounce and a soft bounce?
A hard bounce is permanent: the address does not exist, the domain has no mail server, or the recipient's server rejects you outright. Add the address to a suppression list immediately — retrying only damages your reputation. A soft bounce is temporary: a full mailbox, a message over the size limit, or greylisting, where the server asks you to try again later. Senders normally retry soft bounces for a few days, then treat the address as a hard bounce if it keeps failing.
Why does bounce rate matter for a small team?
Mailbox providers score senders continuously, and bounce rate is one of the clearest inputs they have: a high rate looks like a stale or purchased list. Thresholds vary — SendGrid, for example, tells senders to keep hard bounces under 5% of attempted messages, and much industry guidance treats anything above 2% as a warning sign. For a small team without a deliverability specialist, bounce rate is the first number to watch; the rest is covered in our guide to email deliverability for startups.
How do you keep your bounce rate low?
- Confirm addresses at signup with double opt-in so typos never enter the list.
- Let your platform suppress hard bounces automatically — every serious sender does this by default.
- Prune addresses that have not opened or clicked in months before any large send.
- Set up email authentication — SPF, DKIM, DMARC — since unauthenticated mail is rejected more often.