MailboxValidator
Validate email address to improve deliverability
- Authentication
- API Key
- HTTPS
- Yes
- CORS
- Unknown
- Category
- Data source
- public-apis + marcelscruz
- Documentation / URL
- https://www.mailboxvalidator.com/api-email-free
Overview
MailboxValidator checks email addresses — syntax, domain, and SMTP verification. Auth is an API key.
⚠️ Gotcha (verified 2026-08): an invalid key returns HTTP 200 with empty fields (
"email_address":"","is_verified":"") instead of an error — checkis_verified/email_addressfor emptiness to detect a bad key.
Quick Start
Validate (replace YOUR_KEY):
curl "https://api.mailboxvalidator.com/v1/validation/single?format=json&key=YOUR_KEY&[email protected]"{
"email_address": "[email protected]",
"domain": "gmail.com",
"is_free": "True",
"is_syntax": "True",
"is_domain": "True",
"is_smtp": "True",
"is_verified": "True"
}Authentication
- Register at mailboxvalidator.com → free API key.
- Send it as the
keyquery parameter.
Rate Limits & Notes
- Free tier: ~400 requests/month (check the docs); paid plans scale.
- Single validation returns syntax/domain/SMTP flags; also has bulk and disposable-detection APIs.
- A bad key gives 200 + empty fields (verified) — validate the response.
FAQ
Is MailboxValidator free? Free tier: ~400 requests/month; more is paid.
Why 200 with empty fields? Invalid keys return 200 with blank data (verified) — check the fields.
What does it check? Syntax, domain, SMTP, and disposable status.
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