You can only request a new license key if one of the following has occurred:
function email_exists($email) // ... format check ... // ... MX check ... // ... SMTP RCPT TO ... return $smtp_code === 250;
$domain = substr(strrchr($email, "@"), 1); if (!checkdnsrr($domain, "MX")) // domain has no mail exchanger check if email exists php
This is the only truly reliable “exists” check in PHP. ⚠️ B. Validate email format + domain MX records if (!filter_var($email, FILTER_VALIDATE_EMAIL)) // invalid format function email_exists($email) //
This will fail for Gmail, Outlook, Yahoo, and most corporate servers. | Use Case | Best Approach | |----------|----------------| | Prevent duplicate signups | Check your own database (unique index + SELECT) | | Reduce typos at signup | Format + MX check + email confirmation | | Validate email for contact form | Format + MX + optional DNSBL check | | Bulk email list cleaning | Paid API (NeverBounce, etc.) | | “Does this mailbox exist right now?” | Impossible without sending a verification link | MX check
