Check first, or keep the wrong ones out
The three levels of checking, what list-cleaning services are worth, and the only method that holds.
6 min read
A wrong address costs twice: a bounce, which damages your domain's reputation, and a reader who does not exist. You can spot it before sending — up to a point, and that point is lower than people think.
Three levels, increasingly uncertain
Syntax. There is an @, a domain, no spaces. Instant, free, and it only catches clumsy typos.
The domain. You ask DNS whether that domain can receive mail at all — whether it has an MX record. A domain without one will never receive anything: the address is dead for certain.
The mailbox. You open a connection to the recipient's server and ask whether the address exists, without sending a message. That is where it goes wrong.
What checkers cannot see
Why the third level lies
Many servers answer yes to everything — the « catch-all » setting, common on shared hosting. The address is declared valid, and the message bounces anyway.
Others apply a deliberate delay to a first contact from an unknown sender, to discourage automated sending: the check then fails on a perfectly valid address.
Finally, opening connections to probe thousands of addresses without ever sending a message is behaviour providers notice — and associate with people testing bought lists.
What cleaning services are worth
On an old list that was never cleaned, they help: they remove dead domains and typos, and that lowers the bounce rate of the first send.
On a maintained list they add nothing: bouncing addresses are already removed at every send.
Two caveats. None replaces consent: a valid address is still an address you may have no right to write to. And handing them your list means handing personal data to a third party — who becomes a processor, to be named in your register.
The method that holds: keep the wrong ones out
Email confirmation at signup. A mistyped address never confirms: it does not enter the list. It is the only filter that works every time, because it does not guess — it observes.
Automatic removal after a hard bounce. An address that no longer exists must leave at the first refusal, and never come back through a re-imported file.
Together they keep a list clean without anyone thinking about it, and save paying to clean it.
You can check an address before sending; you cannot rely on it. Confirmation at the door and removal at the first hard bounce beat any verification service.
A list that stays clean by itself
Confirmation at signup, automatic removal at the first hard bounce. 3,000 emails a month, no credit card.
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