How can PHP developers determine if a firewall is blocking SMTP connections in their server environment?

PHP developers can determine if a firewall is blocking SMTP connections by attempting to connect to the SMTP server using PHP's `fsockopen` function. If the connection fails, it is likely that the firewall is blocking SMTP connections. To solve this issue, developers can check the firewall settings to allow SMTP traffic on the server. 

$smtp_server = 'smtp.example.com';
$smtp_port = 25;

if (!$fp = fsockopen($smtp_server, $smtp_port, $errno, $errstr, 5)) {
    echo "SMTP connection failed. Check firewall settings.";
} else {
    echo "SMTP connection successful!";
    fclose($fp);
}

Keywords

PHP firewall SMTP connection server environment

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