Catch-all domain checker
Enter a domain. We probe it with random addresses that cannot exist, then tell you whether the server accepts everything (catch-all) or only real mailboxes. That changes what every verification result means.
We don't save the domain you check.
What a catch-all domain is
A catch-all (or accept-all) domain is configured so its mail server returns 250 OK for every RCPT TO command, even when the mailbox does not exist. The server accepts the message and either silently discards it, routes it to an admin inbox, or bounces it later. The result: a basic SMTP check says deliverable when the address may never receive your email.
Run this before you trust a verification result on a domain. We send RCPT TO to randomly-generated addresses that cannot exist. If the server accepts them all, the domain is catch-all and single-address results there cannot be relied on alone.
What is a catch-all domain?
A catch-all domain accepts mail to every address, real or not. Its mail server returns 250 OK for every recipient, so a basic SMTP check cannot tell a real mailbox from one that does not exist.
How does this tool detect catch-all domains?
We send RCPT TO commands to randomly-generated addresses at the domain that are statistically impossible to exist. If the server accepts them all, the domain is catch-all. If it rejects even one, the server distinguishes valid from invalid mailboxes and verification there is trustworthy.
Why does catch-all cause bounce problems?
On a catch-all domain the server says yes to everything, so a verifier marks every address as deliverable, even ones that do not exist. Those addresses end up on your sending list, bounce after delivery, and damage your sender reputation.
How should I handle catch-all addresses in my list?
Segment them separately and send to the safest, most-engaged contacts first at lower volume, watching the bounce rate. MailCull marks catch-all addresses as Risky, not Deliverable, so you can decide whether to include, suppress, or warm them.