What is an accept-all domain?
An accept-all domain — another name for a catch-all domain — is configured to accept email sent to any address, including ones that don't exist. Because the server never rejects a recipient, you can't confirm an individual mailbox by SMTP alone.
Accept-all and catch-all are the same thing
The terms 'accept-all' and 'catch-all' are used interchangeably. Both describe a mail server that responds positively to every recipient at the domain rather than rejecting unknown addresses. Different verification vendors simply prefer different labels.
The behavior is what matters: a positive SMTP response on an accept-all domain doesn't prove the specific mailbox exists, because the server would have said yes regardless.
Why accept-all domains are common
Companies enable accept-all so that misaddressed mail and departmental aliases still arrive, and many hosting plans turn it on by default. It's especially prevalent on corporate domains, which is exactly where a lot of valuable B2B contacts live.
That prevalence is the challenge: a meaningful share of legitimate business addresses sit on accept-all domains, so you can't simply discard them without losing real prospects.
Verifying addresses on accept-all domains
Since SMTP can't disambiguate individual mailboxes here, the answer is confidence scoring. A verifier evaluates syntax, domain reputation, role-based patterns, and historical signals to estimate how likely the specific address is to be real and deliverable.
Mailbeam detects accept-all domains by probing a random address on the same domain, then returns a capped score and a catch_all_unverifiable reason, so you can set a threshold instead of treating the whole domain as valid or invalid.
Telling accept-all apart from a working server
Two recipients in one session: one plausible, one nonsense. A normal server distinguishes them. An accept-all server cannot.
Normal domain Accept-all domain
--------------------------- ---------------------------
RCPT TO:<sales@example.com> RCPT TO:<sales@example.com>
250 2.1.5 Ok 250 2.1.5 Ok
RCPT TO:<qz7x@example.com> RCPT TO:<qz7x@example.com>
550 5.1.1 User unknown 250 2.1.5 Ok
^ ^
the answer differs the answer never differsAccept-all is not a property you look up, it is a behaviour you detect: send a recipient that cannot exist and see whether the answer changes.
Sources
Checked against these sources on .
In practice
lead@enterprise.com is on an accept-all domain, so the SMTP probe returns accept regardless. Mailbeam reports catchAll: true with a score of 84, reflecting clean syntax and a reputable domain — high enough to accept the lead with confidence rather than discarding a real prospect.
Frequently asked questions
Verify emails with confidence
Mailbeam handles all of this for you — syntax, MX, SMTP, catch-all, and disposable checks in one API call. 1,000 free verifications/month, no credit card.