Amazon SES is the clearest published case. It recommends a bounce rate under 2%, places an account under review at 5% and says it might pause sending at 10%. Complaints have tighter lines: under 0.1% recommended, review at 0.1% and a possible pause at 0.5%. We read these in the SES enforcement FAQ on 24 September 2026.
Mailchimp publishes no number. Its help centre says you get a warning notice once complaints pass its threshold, then a suspension notice, and that suspensions are automatic actions triggered when a single send exceeds industry thresholds. You find out where the line is when you cross it.
Mailbox providers judge a different figure. Gmail's sender guidelines ask you to keep the spam rate reported in Postmaster Tools below 0.3%, to aim for under 0.10%, and to avoid ever reaching 0.30%. Microsoft's Outlook postmaster page sets a volume line rather than a rate: at 5,000 emails a day, SPF, DKIM and DMARC become mandatory.
Put those together and the working rule is simple. Treat 2% as your ceiling for bounces, whatever your platform publishes. You can check where a send landed with the bounce rate calculator.
Why one bad send is enough
Mailchimp's wording matters here: a single send can trigger the action. You don't need a bad month. One campaign to an old list, where years of job changes have turned addresses into 550 replies, is enough to cross a threshold you never saw.
Hard bounces are the part you control. A hard bounce is a permanent failure, usually a 550 for a mailbox that doesn't exist, and on a domain that answers honestly, a verifier finds it before you send. Bulk verification opens an SMTP connection to each domain, asks about the recipient and closes before any message is sent. An address that gets a definite no comes back invalid, and you drop it before the campaign.
Catch-all addresses need their own plan, because their servers accept every recipient during the check. Put them in a separate segment and send to them in small waves while you watch the rate.
Our guides for Amazon SES and Mailchimp cover each platform's reports in detail, and the ZapBounce blog explains the bounce codes you'll see along the way.
Complaints are the other half of the score
The short version
- Keep bounces under 2% on every send, the figure Amazon SES recommends.
- Verify any list older than a few months before it goes into a campaign.
- Watch complaints as closely as bounces: SES reviews at 0.1% and Gmail's ceiling is 0.3%.
Questions people ask
What bounce rate gets an Amazon SES account suspended?
Amazon SES places an account under review at a 5% bounce rate and says it might pause sending at 10%. It recommends staying under 2%, per its enforcement FAQ read on 24 September 2026.
What bounce rate does Mailchimp allow?
Mailchimp publishes no number. Its help centre says suspensions are automatic actions triggered when a single send exceeds industry thresholds, so treat 2% as your ceiling there too.
What spam rate does Gmail allow?
Gmail asks senders to keep the spam rate in Postmaster Tools below 0.3%, to aim for under 0.10%, and to avoid ever reaching 0.30%.
How do I lower my bounce rate before a campaign?
Verify the list first and remove every invalid result. ZapBounce charges $5 for 1,000 checks, never bills unknown results or duplicates, and its credits never expire.