Mailbox Verification opens a real conversation with the receiving mail server and asks, address by address, whether that exact inbox exists — the most accurate check there is, built in-house and run quietly on your saved lists.
The problem
Syntax checks and domain/MX lookups only prove a domain can receive mail somewhere. They can’t tell you that [email protected] is a real, deliverable inbox versus a long-departed employee or a typo that the domain happily accepts and then black-holes. Those addresses pass the cheap checks, bounce on send, and quietly cost you sender reputation.
The market gap
Most “verification” you can buy is a black box: you pay per address, ship your list to a vendor, and get back a verdict you can’t inspect. ZipAudience built its own mailbox prober — we talk to the mail server ourselves, show you the exact reason for every verdict, and keep your list inside the same account where you’ll clean, profile, and send it. No rented API, no list leaving the building.
How we solve it
For each address we resolve the domain’s real mail server and start an SMTP conversation — greeting, sender, then asking the server to accept that specific recipient — and read its answer. We never send a message: the conversation stops before any mail is delivered.
Resolves the domain’s MX records to reach the server that actually handles its mail.
Opens an SMTP handshake and reads whether the server accepts that exact recipient.
The conversation ends before delivery — your contacts get nothing, ever.
Probes a random address; if the server accepts anyone, we mark the domain “can’t confirm.”
Temporary deferrals are flagged and retried instead of being miscounted as dead.
Valid, invalid, or risky — with the reason shown, never an over-promised “valid.”
Mailbox Verification is the truth layer under the AI pipeline. Once a saved list is confirmed inbox-by-inbox, ZipAudience can profile the audience with AI, draft the outreach, and follow up automatically — so your AI campaigns are spending sends only on addresses we’ve actually proven are reachable.
How it works
Upload contacts or save Email Verifier results into My Lists.
Hit “Verify mailboxes” and we start probing servers in the background.
A live progress bar counts checked vs. total — keep working while it runs.
Each contact gets valid / invalid / risky with a reason, ready to filter and send.
Confirms the inbox itself, not just that the domain can receive mail.
Our own prober — your list never leaves your account for a third party.
Every verdict shows why, so risky catch-all and greylist cases are yours to judge.
It’s slow by nature, so it processes in the background and never blocks the app.
No. We open an SMTP conversation and ask the server whether it would accept the recipient, then stop before any message is delivered. Your contacts receive nothing.
Large providers often accept every recipient up front (or temporarily defer) to protect their users from probing, so the server won’t honestly confirm a single mailbox. Rather than claim a false “valid,” we mark those risky and tell you why.
Some domains accept mail to any address, real or not. We detect that by probing a random address first; if the server accepts it, the domain is catch-all and we can’t confirm any individual mailbox — so it’s flagged risky, not silently passed.
Talking to each mail server is far slower than a syntax or DNS check, so it runs in the background in timed slices and picks up where it left off until your whole list is done. The size it’ll process is set by your plan.
Save a list and run mailbox verification — confirm deliverability at the source.
Verify my mailboxesExplore more