An email bounce is a notification that your message couldn't be delivered. There are two kinds — and treating them the same is the fastest way to ruin your sender reputation.
Why this matters: A bounce rate above 2% signals "low list quality" to ISPs. Each unmanaged hard bounce drags your reputation lower the next time you send.
Hard bounce vs soft bounce
| Type | Cause | Action |
|---|---|---|
| Hard bounce | Permanent: bad address, dead domain, blocked | Remove from list immediately |
| Soft bounce | Temporary: full mailbox, server down, oversized | Retry, suppress after 3-5 fails |
Common SMTP bounce codes
- 5.1.1 — recipient address rejected (hard).
- 5.4.1 — recipient does not exist (hard).
- 4.2.2 — mailbox full (soft).
- 4.4.7 — message expired in queue (soft).
- 5.7.1 — message blocked by recipient policy (often hard).
How to manage bounces in Mailpro
- Mailpro auto-classifies every bounce as hard or soft.
- Hard bounces are suppressed automatically — they won't be retried.
- Soft bounces retry up to 5 times, then move to suppressed.
- Export the bounce log per campaign and review unusual spikes.
Stop bounces from hurting deliverability — try Mailpro free
Mailpro categorises and suppresses bounces automatically, so your reputation stays clean. Discover bounce handling · Deliverability hub
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