Codeigniter 3 SMTP with Office 365 - php

Question

I am having difficulties sending email via SMTP using CI3 and Office 365.
My website is hosted with BT.
I found this sample code which I am using, it's the minimum test code for successful email sending over SMTP with Office 365.
In my contact controller I have the following code;
class Contact extends CI_Controller {
public function test(){
$config = [
'protocol' => 'mail',
'smtp_host' => 'smtp.office365.com',
'smtp_user' => 'MY_EMAIL',
'smtp_pass' => 'MY_PASSWORD',
'smtp_crypto' => 'tls',
'newline' => "\r\n",
'smtp_port' => 587,
'mailtype' => 'html'
];
$this->load->library('email', $config);
$this->email->from('MY_FROM_EMAIL');
$this->email->to('MY_TO_EMAIL');
$this->email->subject('Test');
$this->email->message('SMTP sending test');
$sent = $this->email->send();
if ($sent) {
echo 'OK';
} else {
echo $this->email->print_debugger();
}
}
}
When I visit my URL example.com/contact/test I see the following error;
A PHP Error was encountered
Severity: Warning
Message: fsockopen(): unable to connect to smtp.office365.com:587
(Connection timed out)
Filename: libraries/Email.php
Line Number: 1990
Backtrace:
File: .../controllers/Contact.php Line: 118 Function: send
File: ../index.php Line: 341 Function: require_once
Then below that;
The following SMTP error was encountered: 110 Connection timed out
Unable to send email using PHP SMTP. Your server might not be
configured to send mail using this method.
User-Agent: CodeIgniter
Date: Tue, 14 Nov 2017 15:08:27 +0000
etc ...
etc ...
etc ...
I know the login details are correct for the email account as I am able to login and send/receive emails using various email clients.
Any ideas why this is happening, and how I can fix it? Are there any other tests I can carry put in order to help troubleshoot the issue.
I've been stuck at this for days. I don't want to use gmail or any other email provider.