- Email verification, defined
- Email verification is the check that tells you whether an address can receive mail, by testing its syntax, domain and mailbox before you send.
A full check runs in layers, and each one catches something the last one can't. First comes syntax: a legal local part, an @, a real-looking domain. It catches typos like gmial.con and proves nothing about whether anyone reads the inbox.
Next is the domain. A DNS lookup asks for the domain's MX record, the host that takes its mail. No MX and no A record to fall back on means nothing can be delivered there, and the address fails without anyone opening a connection.
Then the SMTP handshake, where the real answer lives. The checker connects to that mail host on port 25 and sends EHLO, then MAIL FROM, then RCPT TO with your address. A 250 means the server accepts it, a 550 means no such user, and a 4xx means try later.
It stops there. The connection closes with QUIT before DATA, so no message is ever sent and the person on your list never sees a thing.
Two more checks sharpen the result. A probe for a random, made-up address at the same domain shows whether the server accepts everything, which makes it a catch-all. And list lookups flag role addresses like info@ or sales@ and throwaway domains from disposable providers.
Some answers stay out of reach for every tool. Yahoo and AOL reply 250 or 252 to every recipient on purpose, greylisting servers stall first-time senders, and Microsoft 365 and Gmail block probes from cloud IPs. So a result worth trusting reports two numbers: how much of your list got a verdict, and how right those verdicts are. Why verifiers disagree shows how far apart tools land on the same file.
How ZapBounce reports it
ZapBounce runs its own SMTP check over port 25 and returns one of four results for every address: valid, invalid, catch_all or unknown, with role, disposable and free_provider as separate flags. You can check one address at a time through the API with POST /v1/verify, or upload a whole list on bulk. unknown results and duplicates are never billed, credits never expire, and every account gets 100 free checks a month with no card.
Email verification: common questions
Does email verification send an email?
No. The check opens an SMTP connection, asks about the recipient with RCPT TO, and closes before the DATA step. No message is created, so the person never receives anything.
Is email verification the same as email validation?
In practice the two terms are used for the same job. Some tools say validation for the format check alone and verification for the mailbox check, so read which layers a tool actually runs before you compare prices.
What accuracy can email verification reach?
On domains that answer honestly, 95 to 98% is the defensible ceiling for any verifier. Catch-all domains, Yahoo and servers that block probes can't be resolved at mailbox level, so a headline accuracy figure means little without the share of the list it covers.
When should I verify a list?
Before the first send from any list you didn't collect yourself, and again before a campaign to a file that has sat unused for months. Signup forms get the same check at the moment someone types their address.