What happens in those two seconds.
Six steps, no email sent, and an honest answer at the end — including when the honest answer is that nobody would tell us.
- 01
Syntax
Missing an @, a stray space, a domain that is not a domain. These are caught instantly, before we touch the network, and they cost you nothing.
- 02
Domain and mail server
We find out where mail for that domain is supposed to go. A domain with no mail server cannot receive anything, however impressive its website looks.
- 03
The conversation
We connect to that server and ask, in its own protocol, whether it would accept mail for this one person. Then we hang up. The command that actually delivers a message is never sent — this is the part people worry about, and it simply does not happen.
- 04
A second address
We also ask about an address we invented, which cannot possibly exist. If the server says yes to that as well, it says yes to everything, and its answer about your address was worthless. We tell you instead of pretending otherwise.
- 05
A second pass
Plenty of servers stall the first time anyone asks — it is a standard anti-spam tactic. We wait and ask again, automatically, instead of writing the address off as bad.
- 06
The verdict
One of four, with a reason code and a recommended action. If the server never gave us a straight answer, you get unknown and we charge you nothing.
What cannot be known
Nobody can confirm one mailbox on a domain that accepts every address — not us, not anyone. And no verifier on earth can tell you whether a real mailbox is still read by a real person. Any service claiming a number on either is inferring and calling it a fact.
Where we cannot get an answer you get unknown, free of charge. It makes our deliverable count look smaller than a competitor who guesses. It also means the number you do get is one you can trust.
Every result code and what it means →