Bounce rate is the single most direct signal mailbox providers use to judge senders: under 2% you are fine, above 5% your account is at risk. And since roughly a quarter of B2B addresses go stale every year, staying under the line is an ongoing practice, not a one-time cleanup.
Why 2% is the line
Mailbox providers treat bounce rate as a direct measure of list hygiene. Under 2%, you are indistinguishable from a legitimate sender. At 3–5%, filters start diverting mail to spam. Above 5%, sending platforms themselves (Google Workspace, Outlook, most ESPs) may suspend your account. The difference between 1% and 6% is usually not luck — it is whether the list was verified before sending.
Hard bounces vs soft bounces
- Hard bounce: permanent failure — the address does not exist, the domain has no mail server, or the recipient blocked you. Remove immediately and never resend.
- Soft bounce: temporary — full mailbox, server timeout, message too large. Retry once or twice; treat repeat soft-bouncers as hard.
- Reputation damage comes overwhelmingly from hard bounces: each one tells the provider you are sending to addresses you have no relationship with.
Where bad addresses come from
- Decay: roughly 25–30% of B2B email addresses go stale every year as people change jobs — a list verified 12 months ago is not verified
- Typos at capture: form fills and manual entry (gamil.com, .con)
- Catch-all domains: the server accepts everything at SMTP time, then bounces internally after you have already been scored
- Purchased lists from unvetted brokers: often padded with pattern-guessed addresses that were never real
The pre-send checklist that keeps you under 2%
- Verify every list before every campaign — syntax, MX records, and mailbox existence. Not just new lists: re-verify anything older than 3 months.
- Segment out catch-alls: send to verified addresses first; treat catch-all results as a separate, lower-volume segment
- Remove role addresses (info@, sales@) from cold outreach — higher complaint rates and lower engagement
- Drop disposable domains entirely
- Monitor per-campaign: a sudden bounce spike on one segment means a bad data source — find it before the next send
Fixing a damaged reputation
If bounces already spiked: stop sending from the affected domain, verify and prune the entire list, then re-enter a mini-warmup at reduced volume to your most engaged segment for 2–3 weeks — engagement signals rebuild trust the same way they built it originally. Our warmup guide covers the schedule.
Every list you run through the Sendburg platform is verified automatically before export — or check any list up to 100 addresses free with the free email verifier.