Your email list bounced 30% — what to do first

Stop sending to that list today. A thirty percent hard-bounce rate is not a copy problem or a subject-line problem — it means roughly one in three addresses was never deliverable, and continuing to send keeps burning the domain reputation you need for everything else.

Then diagnose by domain rather than by address. Group the bounces, check MX records, and you will usually find that a handful of dead domains account for most of the failures.

Step 1: separate hard from soft bounces

Hard means permanent: no such domain, no such user, address rejected. Remove these immediately and never send again. Soft means temporary: mailbox full, server busy, message too large. One soft bounce is noise; the same address soft-bouncing for three campaigns is a dead mailbox.

Step 2: find the dead domains

Export the bounced addresses, dedupe them, and take the unique domain list. Then check which domains have no MX record. Domains with no mail server cannot accept mail from anyone, so every address on them is guaranteed to fail — you can delete them with no judgement call at all.

If a large share of your list sits on one or two domains you have never heard of, that is the fingerprint of a purchased or scraped list, and the rest of it deserves the same suspicion.

Step 3: check what the bounce messages said

Your sending platform logs the SMTP response. 550 5.1.1 user unknown means the domain exists but the mailbox doesn't — those are guesses, and they need a mailbox-level verifier. 550 5.4.1 or a connection timeout usually points at the receiving server refusing you, which is a reputation problem, not a list problem.

Step 4: restart small

After removing the dead weight, send the next campaign to a few hundred of your most engaged recipients first. Watch bounces and complaints for 24 hours before scaling. Sending platforms that saw a thirty percent bounce rate will be watching your next few sends closely.

Step 5: fix the source

Ask where the list came from. If it was purchased or scraped, the damage will repeat on the next purchase, because the supplier's data is the same age and the same provenance. The durable fix is a signup path you control and a quarterly cleanup cadence.

Check your own list in about 30 seconds. Paste or drop a CSV — duplicates, typos, role addresses and dead domains, all handled in your browser. Free for the first 100 addresses, $19 once for unlimited.

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Common questions

Can I just re-verify the whole list instead?

You can, and it will tell you which mailboxes exist if you pay a per-address verifier. But start with MX checking: it is instant, free and removes the dead-domain share, which after a 30% bounce rate is usually the majority.

Should I tell my provider before resending?

If your account is already flagged or throttled, yes. Support can tell you what they saw and whether you are on a probation period — information you cannot get from the bounce log.

Last updated 2026-10-23.