How to Verify Gmail Email Addresses via API (2026 Guide)

Most email verification APIs return UNKNOWN for Gmail addresses. CheckMail1 uses provider-specific SMTP logic to verify Gmail, Outlook, Yahoo, iCloud and 150+ providers accurately.

Why Gmail Returns UNKNOWN

Gmail blocks standard SMTP probes at the server level. Most tools give up and return UNKNOWN. CheckMail1 uses provider-specific handshake patterns that work correctly with Gmail.

Quick Start

curl 'https://checkmail1.com/api/[email protected]' \
  -H 'Authorization: Bearer YOUR_API_KEY'

Response:

{"email":"[email protected]","valid":true,"result":"valid","provider":"gmail","response_time_ms":143}

Supported Providers

CheckMail1 supports 150+ providers: Gmail, Outlook, Yahoo, iCloud, ProtonMail, Yandex, QQ, Naver and more.

Pricing

Pay-as-you-go from $5 per 1,000 checks. Credits never expire. Start with 100 free credits — no credit card required.