Glossary
Email verification
Email verification checks whether an email address exists and can receive mail before you send to it. It tests syntax, the domain's MX records and the mailbox itself, then labels each address valid, invalid, catch-all or unknown.
What Is Email Verification?
In short A verifier runs its checks in order.
First syntax, then the domain: does it exist and publish MX records? Then the mailbox. The verifier opens an SMTP session with the domain's mail server, names the address as a recipient (the RCPT TO step) and reads the reply. Under RFC 5321 a server answers 550 when it knows the address can't receive mail. The verifier disconnects before any message is sent.
The mailbox check has limits. RFC 5321 lets a server accept a recipient during the conversation and report problems later, and a catch-all server accepts every address, so a yes does not prove the mailbox exists. VRFY, the SMTP command meant for checking addresses, can be switched off, and a server that disables it must answer 252, which confirms nothing.
Email Verification Example
Example: a team uploads 5,000 contacts. Verification marks 4,100 valid, 350 invalid, 450 catch-all and 100 unknown. It sends to the 4,100 first, drops the 350 and tests the catch-all group later in small batches from a single mailbox.
Email Verification in Practice
For cold email, verification protects your sender reputation. Hard bounces tell mailbox providers you are mailing addresses that don't exist, the pattern of a bought or scraped list. Verify right before a campaign: people change jobs, so a list checked months ago has gone stale.
FAQ
What is email verification?
A check that an email address exists and can receive mail, done before you send to it. It covers syntax, the domain's mail servers and the mailbox itself.
How does email verification work without sending an email?
The verifier connects to the domain's mail server over SMTP, names the address as a recipient and reads the reply. A 550 reply means the server knows the address can't receive mail. The verifier then ends the session before any message is sent.
What do catch-all and unknown mean in email verification?
Catch-all means the domain's server accepts every address, so the verifier can't confirm this one. Unknown means the server gave no clear answer, for example because it delays or limits unfamiliar connections. Treat both as risky.
Is email verification the same as email validation?
The terms are used interchangeably. Some tools use validation for the syntax and domain checks and verification for the full mailbox check.
How often should you verify an email list?
Right before each campaign that uses it. B2B contact data goes stale as people change jobs, so a list verified months ago will bounce more than it did then.
Do This in Ken
Do This in Ken
Ken Search verifies every email it finds and charges 1 credit only when the address comes back valid, so you don't pay for addresses that fail verification.
- Module
- Ken Search
- Open in Ken
- /features
The new Ken opens to the waiting list in batches.
Related
- GTM Glossary
Every GTM term, grouped by topic.
- Email bounce rate
- Catch-all email
- Sender reputation
- MX record
- Waterfall enrichment
- Data enrichment
- Ken
Sources
| Source | Checked |
|---|---|
| RFC 5321: Simple Mail Transfer Protocol | |
| RFC 3463: Enhanced Mail System Status Codes |
Changelog
- Page published.