Hello everyone,

I'm trying to send emails via Zoho SMTP using PHPMailer on my shared hosting environment. I've tried both port 465 (ssl) and 587 (tls), and I even added SMTPOptions to bypass SSL verification just in case it was an SSL certificate issue. However, the connection drops instantly. 

Here is my current configuration:

$mail->isSMTP();

$mail->Host       = 'smtppro.zoho.com';

$mail->SMTPAuth   = true; 

$mail->SMTPOptions = array(

    'ssl' => array(

        'verify_peer' => false,

        'verify_peer_name' => false,

        'allow_self_signed' => true

    )

);

$mail->Username   = '<myemail>';

$mail->Password   = '<mypassword>'; // application password

$mail->SMTPSecure = 'ssl';

$mail->Port       = 465;

$mail->CharSet    = 'UTF-8'; 

The debug output (SMTPDebug = 2) is very short, meaning it fails at the TCP level before any SMTP negotiation happens:

"SMTP ERROR: Failed to connect to server: Connection refused (111) SMTP Error: Could not connect to SMTP host. Failed to connect to server"

My hosting provider insists that outbound ports 465 and 587 are open. My questions are:

1. Could this be caused by SELinux blocking network connections for the web server (e.g., httpd_can_network_connect = 0)?

2. Is it possible that the server's IPv6 configuration is broken, and PHPMailer is trying to resolve Zoho via IPv6?

3. How can I definitively prove to the hosting provider whether this is an OS/Firewall issue on their end?

Thanks in advance for your insights!