What could be the potential reasons for receiving the error message "unexpected response 550 to RCPT TO command" when sending an email to an address within the same domain?

The error message "unexpected response 550 to RCPT TO command" typically indicates that the recipient email address is not valid or does not exist within the same domain. This could be due to a typo in the email address, the recipient's mailbox being full, or the recipient's email server rejecting the email. To solve this issue, double-check the recipient email address for any errors and ensure that the mailbox is active and able to receive emails. 

// Example PHP code snippet to check for valid recipient email address before sending the email
$to = "recipient@example.com";

// Check if the recipient email address is valid
if(filter_var($to, FILTER_VALIDATE_EMAIL)) {
    // Send the email
    mail($to, $subject, $message, $headers);
} else {
    echo "Error: Invalid recipient email address";
}

Keywords

PHP email SMTP error message domain

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