How email verification works, check by check
Verification is a short conversation with the receiving mail server, plus a few checks you can run before you even start it. Here is each step, what it proves and where it stops being able to prove anything.
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1. Syntax
The first check costs nothing and removes a surprising share of a bought list. An address has to be shaped the way the mail standard requires: one at sign, a local part within the allowed characters and length, a domain that is a valid domain name. Typos, trailing commas from a spreadsheet and addresses with a space in the middle die here.
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2. Domain and MX records
Next we ask the domain name system which servers receive mail for that domain. If a domain publishes no MX records and no usable fallback, it accepts no mail, and every address on it bounces regardless of how correct it looks. The MX hosts also tell us which provider runs the mailbox, which matters because providers behave differently in the next step.
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3. The mailbox at the server
We open a conversation with the receiving server the way a sending server would, and ask whether it will accept mail for that specific mailbox. We stop before sending anything, so the person on the other end never sees a message. The server's answer is the strongest evidence anyone can get from the outside: it either accepts the recipient or it does not.
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4. Catch-all and risk flags
Some servers accept every recipient on the domain, whether the mailbox exists or not. That is a catch-all, and on a catch-all domain step three proves nothing. We detect it by asking about an address that cannot exist and seeing whether the server accepts that too. We also flag role addresses, disposable domains and consumer mailboxes, which are all deliverable and all mean something different for a B2B list.
Four statuses, four decisions
| Status | What happened | What to do |
|---|---|---|
| Deliverable | The server accepted this specific mailbox | Send to it |
| Undeliverable | Syntax, the domain or the mailbox failed | Drop it and never retry it |
| Catch-all | The server accepts every address on the domain | Keep it out of cold sequences, or send with a warmed domain and low volume |
| Risky | The mailbox works but it is a role, disposable or consumer address | Decide by list, not by row |
Being honest about the ceiling
No external verifier can see inside a mailbox. These are the cases where anyone claiming certainty is selling you a guess.
- A catch-all domain hides whether one mailbox exists. We label it rather than guessing, and a catch-all row does not count as a verified find.
- Some providers deliberately accept every recipient during the conversation and bounce afterwards, to stop exactly this kind of checking. The result is the same as catch-all and we treat it the same way.
- A greylisting server defers the first attempt from an unknown sender. We retry, and if the answer stays unclear we say unclear.
- A full mailbox, an out of office or an autoresponder tells you nothing about whether mail arrives. Only the send tells you that.
- Verification says the mailbox exists. It says nothing about whether the person wants your email, which is still your job.
A found address without verification is just a pattern
When we resolve an address from a name and a domain, the ranked pattern is a hypothesis. The verification steps above are what turn it into a row you can send to. That is also why a find that fails verification costs nothing on any plan: you did not get an answer, so you should not pay for one.
Read find email address by name for the pattern side, and email verifier for the check set in full.