Every email verification tool runs an address through a series of checks. The trouble is, not every tool tells you which checks it actually performs — some quietly stop at the domain level and still call the result "verified." Here's what each layer really does.
Syntax Validation
Confirms the address is formatted correctly per RFC 5322 — catches typos like missing @ symbols or invalid characters.
LiveMX Record Lookup
Checks the domain's DNS for a mail exchange record, confirming it's set up to receive email at all.
LiveDisposable Detection
Flags addresses from known temporary/throwaway email providers.
LiveRole Account Detection
Flags generic addresses like info@ or support@ that aren't tied to one person.
LiveSMTP Mailbox Check
Connects to the receiving mail server to confirm the specific mailbox exists — not just the domain.
LiveWhere SMTP verification fits in
SMTP verification goes a step further: it opens a connection to the recipient's mail server and asks whether a specific mailbox would accept mail — without actually sending anything. It's the closest a tool can get to proving a mailbox is real.
It's also the hardest layer to get right. Many mail servers respond the same way to every address at a domain (called a "catch-all" setup) specifically to prevent this kind of probing, and some providers rate-limit or block verification traffic outright. A verifier that skips this complexity and just claims "99% accuracy" is usually skipping the check, not solving it.
Mail Bounce Pro's current status
All five checks are live today: Syntax validation, MX record lookup, disposable detection, role-account detection, and a live SMTP mailbox check against the receiving mail server. Some providers rate-limit or block automated SMTP probes — in those cases, the result is labeled UNKNOWN rather than guessed.
Why a "valid" email can still bounce
If a tool only checks syntax, MX, and domain reputation, an address can pass every one of those checks and still bounce — the mailbox might not exist, might be full, or the domain might be a catch-all that accepts everything at first and rejects it later in the delivery chain. Understanding which layer a verifier stops at tells you how much to trust a "valid" result.
Frequently asked questions
What does email verification actually check?
Syntax, MX records, disposable-domain status, and role-account patterns at minimum. More thorough tools add a live SMTP check to test the specific mailbox.
Does passing verification mean the mailbox definitely exists?
Only if the tool performs an SMTP-level check. Domain-level checks alone confirm the domain can receive mail, not that a specific inbox is real.
What is SMTP verification?
A live handshake with the recipient's mail server to ask if a mailbox would accept mail, without sending a message. It's blocked or masked by some servers via catch-all configurations.
Why do some valid-looking emails still bounce?
Because passing syntax/MX/domain checks doesn't guarantee the specific mailbox is active, not full, and not behind a catch-all that later rejects the message.