TL;DR
- B2B lists contain catch-all domains that accept any address, so a verifier can't confirm the person. Hunter's sample: 38% of domains, bouncing 27% vs 1% for valid.
- Security gateways and role addresses add more uncertainty.
- A good verifier labels these cases instead of calling them valid. We label catch-all, role and disposable separately under "risky".
Catch-all domains
A catch-all domain tells the sender "yes" to every address, including ones that don't exist, then decides later what to do with the mail. Companies set this up so mistyped addresses still reach someone. A verifier asks the server whether the mailbox exists, and gets a yes for any address, so it can't tell a real person from a made-up one. Hunter's published study (checked 2026-10-17) found 38% of the domains in its sample were accept-all, and addresses on them bounced 27% of the time against 1% for valid addresses. Consumer providers like Gmail don't behave this way, which is why B2B is harder.
We detect catch-alls by asking about a random address too. If it's accepted, the domain is catch-all. See what a catch-all is and how to send to them safely.
Security gateways
Some companies route mail through a security gateway that sits in front of the real mail server. A gateway can accept every address at the door, which looks like a catch-all, or give vague answers. Senders on cold-email forums report that results for gateway-protected domains are less reliable across verifiers. We can't give you a share or a guarantee: treat results for domains behind a gateway with the same care as catch-alls, and watch your first sends.
Role addresses
B2B lists scraped from websites are full of info@, sales@ and support@. These reach a team, not the person, and are more likely to be monitored by filters or complaint-happy staff.
We label them low_quality under risky. Usually leave them out of cold campaigns. See role-based addresses.
Job changes
Work addresses die when people leave. That is why B2B data goes stale; see list decay and how often to verify.
What the results look like
| Situation | Mail Exchange result | What to do |
|---|---|---|
| Server confirms the mailbox | deliverable | Send |
| Catch-all domain | risky: low_deliverability (accept_all true) | Separate campaign or skip |
| Shared inbox (info@) | risky: low_quality | Usually leave out |
| Mailbox rejected, bad domain, bad syntax | undeliverable | Remove |
| No definite answer | unknown | Retry later; credit refunded |
The checks behind this are on how it works. We never send an email to the address.
A B2B workflow
- Export from your lead source ( Apollo and others), even if marked "verified".
- Verify at Mail Exchange.
- Send deliverable first. Put catch-alls in a separate, slower campaign from older inboxes.
- Watch the first few hundred sends and stop a segment if bounces climb past your threshold.