Why Can\'t My PHPMailer Connect to the SMTP Host, Even Though Other Clients Can?

PHPMailer SMTP Host Connectivity Issue

Upon using PHPMailer, users may encounter the frustrating error message "SMTP Error: Could not connect to SMTP host." This issue can be particularly puzzling if email can be successfully sent via other clients like Thunderbird.

To diagnose the problem, compare your current SMTP settings with those from previous projects where PHPMailer worked successfully. One key difference is the "Connection Security" setting. In the provided example, Thunderbird uses "STARTTLS" while the previous PHPMailer project used "SSL/TLS."

If the "Connection Security" setting is misconfigured, the following code snippet can be added to the PHPMailer configuration:

$mail->SMTPOptions = array(
    'ssl' => array(
        'verify_peer' => false,
        'verify_peer_name' => false,
        'allow_self_signed' => true
    )
);

However, it's important to note that this is only a temporary workaround. The underlying issue should be addressed by ensuring the server certificate is valid and properly configured. This may involve updating the certificate or replacing it with a trusted one.

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