How the email checker works

This tool checks whether a recipient mail server accepts an address. It does not send an email, save email content, or use a third-party verification API.

Verification flow

You enter an email address, for example name@example.com.
The checker reads the domain and looks up its DNS MX records. MX records identify the servers that receive mail for that domain.
It connects to one of those recipient mail servers on SMTP port 25.
It performs a short SMTP conversation, then disconnects before any message body is sent.

EHLO checker domain MAIL FROM:<sender identity> RCPT TO:<address being checked> QUIT

The checker never sends the SMTP DATA command. That command is where an actual email subject and body would be submitted.

Result meanings

Accepted by mail server: the recipient server returned SMTP 250 or 251. This is a positive deliverability signal.
Rejected by mail server: the recipient server returned a permanent 5xx response, such as 550. This commonly means the mailbox is unavailable or does not exist.
Could not confirm: the server timed out, blocked the check, or returned a temporary/unclear response.
Invalid domain: the domain has no mail-exchanger (MX) record.

Important limitations

A positive SMTP response is not a 100% guarantee that a person reads the mailbox. Providers may use catch-all addresses, privacy protections, rate limits, or temporary blocks. For account ownership confirmation, send an opt-in verification email with a one-time link.

Hosting requirements

PHP 8+ with socket access.
Outbound SMTP port 25 must be open from the server.
A stable server IP and reverse DNS improve acceptance by recipient mail servers.
Public deployments should add rate limiting and abuse protection.