PHP Mailer can't send emails using my work internet connection - php

Question

i'm developing a website to send reminders to employees in my company using phpmailer, the emails are working fine, but when i connect to the workplace internet connection it stops working with no errors but:
Connection: opening to smtp.mail.yahoo.com:587, timeout=300, options=array ( )
i'm guessing it might be a closed port, so i tried using 587 and 25.
i'm not that good in networking, is there's any way i can know what is the exact error?
function SendOutlook(){
//$recipient = 'xxxxx#yahoo.com';
require 'PHPMailer/PHPMailerAutoload.php';
$Emp_recipient = "employee#yahoo.com";
$mail = new PHPMailer;
$mail->SMTPDebug = 4; // Enable verbose debug output
$mail->isSMTP(); // Set mailer to use SMTP
$mail->Host = "smtp.mail.yahoo.com"; // Specify main and backup SMTP servers
$mail->SMTPAuth = true; // Enable SMTP authentication
$mail->Username = 'xxxxx#yahoo.com'; // SMTP username (server username)
$mail->Password = 'xxxxx'; // SMTP password
$mail->SMTPSecure = 'tls'; // Enable TLS encryption, `ssl` also accepted
$mail->Port = 587; // TCP port to connect to
$mail->setFrom('xxxxx#yahoo.com', 'One');
$mail->addAddress($Emp_recipient,"name"); // Add a recipient
$mail->isHTML(true); // Set email format to HTML
$mail->Subject = 'test';
$mail->Body = "scheduled on your outlook calender";
if(!$mail->send()) {
echo 'Message could not be sent.';
echo 'Mailer Error: ' . $mail->ErrorInfo;
exit();
}else {
echo '<p>Message has been sent</p>';
}
echo !extension_loaded('openssl')?"Not Available":"Available";
}