Help & FAQ
Everything you need to read a SkipBounce report and act on it with confidence.
The four statuses
Every address gets exactly one of four verdicts. Two are definitive, two are honest shades of grey — and the grey ones exist because mail servers sometimes refuse to give a straight answer. A validator that never says "risky" or "unknown" is guessing on your behalf.
The receiving mail server explicitly confirmed the mailbox exists and accepts mail. Safe to send.
Hard failure: invalid syntax, a domain that can't receive mail, or the server rejected the mailbox. Sending will bounce — remove these before your next campaign.
Mail will probably arrive, but with a caveat: the domain accepts everything (catch-all), the address is a role account (post@, info@), or it's a disposable inbox. Send with judgement.
The server gave no definitive answer — timeout, greylisting, or an evasive configuration. We report that honestly instead of guessing. Treat as risky until re-checked.
What to do with each
Send with confidence. The receiving server confirmed the exact mailbox. This is the list you export as "Deliverable only".
Remove or suppress before your next send — every one of these is a guaranteed bounce that damages your sender reputation. Never "try anyway".
Use judgement. These addresses usually accept mail, but something lowers the trust: check the flag to see what. For a newsletter, keeping risky addresses is usually fine; for a cold outreach campaign or a small warm-up domain, drop them. The "Cleaned list" export includes deliverable + risky.
Don't count them as good. The server refused to give a clear answer this time — often greylisting that resolves itself. Re-validate unknowns after a day or two; many turn into a definitive answer on the second pass.
The quality score (0–100)
The score compresses everything we learned into one number. A clean, confirmed mailbox lands at 97. Hard failures sit near 0. In between, each caveat costs points: a catch-all domain caps the score around 62, a role account subtracts, a disposable domain drops it to 15 or below, a blacklist hit costs 10. Use it to sort within a status — two risky addresses aren't equally risky.
Flags explained
catch-all | The domain accepts mail for any address, so a positive answer proves nothing about this specific mailbox. |
disposable | A temporary throwaway inbox (e.g. Mailinator). Useless for marketing — treat as bad. |
free-provider | A personal freemail address (Gmail, Hotmail, …). Fine to send to; just not a business address. |
role-account | A shared function address like post@ or info@, read by nobody in particular. High complaint risk. |
blacklisted | The domain or its mail server appears on a public spam blacklist. |
How a check actually works
- Syntax & typos — RFC-grade parsing, plus a typo detector that suggests corrections for misspelled major domains (gamil.com → gmail.com).
- Lists — the domain is checked against disposable-email and free-provider lists, and the local part against known role prefixes.
- DNS — we resolve the domain's MX records. No mail server = no mailbox, undeliverable.
- Live SMTP conversation — our server connects to the domain's mail server and asks, in the protocol mail servers use with each other, whether the mailbox accepts mail. We hang up before anything is sent. The server's literal reply is what you see in the "SMTP response" column.
- Catch-all probe — in the same conversation we also ask about a random address; if that's accepted too, the domain is flagged catch-all and the score is capped.
- Blacklists — the domain and its mail server IP are screened against public DNS blocklists.
FAQ
- Why do some Microsoft 365 / Outlook domains come back risky or unknown?
- Many Microsoft-hosted domains are configured to accept mail for any address and only bounce later, or to answer evasively. When a server behaves that way there is no honest way to verify a single mailbox — so we say risky (catch-all) or unknown instead of pretending. Every serious validator has this limitation; the difference is whether they admit it.
- An address I know is real came back undeliverable. How?
- Rare, but possible: the mail server may have been temporarily misconfigured, or it rejects verification probes from unknown senders. Check the SMTP response shown in the report — it's the server's literal answer. If it's a clear "user unknown", the mailbox really did not exist at that moment as far as its own server is concerned.
- Does validating an address send an email to it?
- No. We open an SMTP conversation and stop before any message content is transmitted. The mailbox owner sees nothing, receives nothing.
- Why did my catch-all domain score only 62 even though it accepted the address?
- Because the same server also accepted a random address like zx9k2q8w@ — meaning acceptance proves nothing. We cap the score on catch-all domains so you don't over-trust them.
- How long do you keep my results?
- Bulk jobs and their results are deleted automatically 48 hours after completion, and you can delete any job immediately. The validation servers themselves never store addresses at all.
- What counts against my monthly quota?
- Each unique address checked counts once — dashboard, bulk, API, or Klaviyo analysis. Duplicates within one job are removed before counting. Failed checks (engine unavailable) are refunded.
- What's the difference between Suppress and Tag in the Klaviyo cleaning?
- Suppress uses Klaviyo's own suppression system: the profiles stop receiving campaigns and stop counting toward your Klaviyo bill (reversible in Klaviyo). Tag only sets a skipbounce_status property on the profiles so you can build a segment and decide yourself — nothing changes until you act on it.
- Should I delete risky addresses from my list?
- Usually no. Role accounts and catch-alls often are real readers. The pragmatic approach: keep them in regular sends, exclude them from cold outreach and from warm-up phases on new domains, and watch engagement.
Didn't find your answer? Email hello@skipbounce.com — or check the API documentation for developer questions.