7 levels of verification:
- By RFC standards.
- By service email (no-reply@, no-spam@, …).
- MX records exist.
- By disposable/temporary email service.
- By spam catchers (like abusix.com network members).
- Connects to email service via standard protocol (SMTP) to check account exists.
- Connects to email service via internal api to check account banned or blocked (supports: Gmail, Mail.Ru, iCloud, Hotmail, Yahoo, Outlook, Rambler, Yandex and more).