Hard bounces vs soft bounces: the thresholds that get you blocked

Every bounce is a mailbox provider telling you something. The senders who get blocked are the ones who don't listen.

Here's the plain-English version of what bounces mean, which ones matter, and the numbers you need to stay under.

Hard bounces: the address is dead

A hard bounce is a permanent failure. The address doesn't exist, the domain doesn't exist, or the mailbox was deleted. Typical causes:

• Typos at signup (gmial.com is doing heavy traffic somewhere)
• Employees who left — their name@company.com died with their badge
• Old lists — B2B addresses decay at roughly 20–30% per year
• Fake signups — asdf@asdf.com from someone who wanted your lead magnet, not your emails

The rule for hard bounces is absolute: never mail the address again. A sender who keeps hitting dead addresses looks exactly like a spammer running a scraped list, and mailbox providers score you accordingly.

Soft bounces: temporary — probably

A soft bounce is a temporary failure: mailbox full, server down, message too large, or the receiver deferring you ("greylisting") to see if you retry like a legitimate server.

Soft bounces deserve retries — but not forever. An address that soft-bounces on every send for weeks is a hard bounce wearing a disguise. Sensible policy: retry for a few days, and if an address soft-bounces across several consecutive campaigns, suppress it like a hard bounce.

The numbers that matter

• Under 2% bounce rate — the widely used industry ceiling. Amazon SES, the infrastructure layer under many platforms including ours, puts senders under review well below the double digits.
• Under 1% — where you should actually live.
• 5%+ — you have a list problem, and your emails are likely already landing in spam even for the valid addresses.

That last point is the part people miss: bounce rate doesn't just risk your account, it drags down deliverability for everyone else on your list. Mailbox providers treat a high-bounce sender's mail as suspect across the board.

Where bounces really come from

Bounce spikes almost never come from your regular sending. They come from importing a list that sat in a drawer. Six months of decay is enough to push a clean list past 2%. This is why the single highest-leverage deliverability habit is boring: verify before you send — always for imported lists, and periodically for segments you haven't mailed in months.

Verification catches dead addresses before the mailbox provider does. The difference matters enormously: a verified-and-removed address costs you nothing; a hard bounce costs you reputation.

What your platform should do about it

You shouldn't be managing this by hand. At minimum, your email platform should:

1. Suppress hard bounces automatically — permanently, account-wide
2. Retry soft bounces sensibly, then suppress repeat offenders
3. Let you verify lists before sending — this is where we're opinionated: PristineSend includes a free monthly verification allowance on every plan, because clean lists are the foundation everything else sits on
4. Watch the trend — a bounce spike mid-campaign should trigger alarms, not a post-mortem

The bottom line

Bounces are the most controllable deliverability metric you have. Dead addresses are detectable before you send — so a high bounce rate isn't bad luck, it's skipped hygiene. Verify imports, suppress failures automatically, and 2% becomes a line you never think about.

Send to clean lists only →