How to Verify an Email Address
Three ways to verify an email address: a single-address check, a bulk list upload, and the API. What each one proves, and how to read the result.
You have an address, say [email protected], and you want to know whether mail sent there will land. Verifying it means asking the receiving mail server whether the mailbox exists, without ever delivering a message. Sending a test is the worst way to find out: if the address is dead, you have just told that server you mail unknown people, which is exactly what hurts your sender reputation.
There are three ways to do it, depending on how many addresses you have.
01The three ways to verify
1. Check one address. Paste a single address into a verifier and get an answer in a second or two. Use the free email verifier, no account needed. It runs the full pipeline on that one address: syntax, MX records, an SMTP probe of the mailbox, catch-all detection, and the Microsoft 365 path where it applies. You see the MX record it found and the raw server reply behind the verdict, so you can audit exactly why it passed or failed. This is the fastest way to settle a single "is this real?" question.
2. Upload a list. When you have a CSV of hundreds or thousands of addresses, the same engine runs over the whole file and hands back a verdict per row. This is the list-cleaning workflow: cull the dead addresses, segment the uncertain ones, and send only to the confident set. See how to use MailCull for the upload-to-export walkthrough.
3. Call the API. If verification needs to happen inside your own product, at signup, before a send, or in a CRM sync, the API verifies an address on demand and returns the same verdict and evidence as a JSON response. There is also an MCP server so an MCP client can run checks directly.
All three run the same checks and return the same four-word verdict, so the answer does not change based on how you ask.
02What the verdict tells you
Whichever way you ask, every check resolves to one of four honest statuses: deliverable (safe to send), risky (accepts mail but with a caveat, such as a catch-all or a role address), undeliverable (cull it), or unknown (the server would not give a straight answer). The full vocabulary and the edge cases behind each one live in the without-sending guide.
No verifier is perfect. MailCull states 98% real-world accuracy, and anything it genuinely cannot resolve comes back as risky or unknown rather than a confident false positive. Every verdict ships with its evidence, the SMTP reply and the MX record it found, so you can audit the result instead of trusting a checkmark.
03Going deeper
This is the overview. If you want the full mechanics of how an address gets checked without a message ever being sent, the check layers, what each one proves, and where they break down, read can you verify an email address without sending one.
For the parts that trip up most lists:
- How to check MX records covers the domain-level DNS check.
- How to check a catch-all domain covers the hardest case, a server that says yes to everything.
- How to detect disposable emails covers throwaway-inbox domains.
04Verify an address now
Run the full check on a single address, free and with no account, using the free email verifier. For a whole list or an API key, start free with 500 validation credits a month and no credit card.
Start with 500 free validation credits. No card.
Both Free and Pro run the same scan engine, full SMTP probe, MX lookup, typo, disposable, domain checks, and the evidence chain on every verdict. The difference is the monthly credit pool (Free=500, Pro=10,000, Max=75,000) plus Pro's API and MCP access.