How to Fix \"SSL3_GET_SERVER_CERTIFICATE: certificate verify failed\" Errors in PHPMailer?

Troubleshoot SSL Certificate Verification Failures in PHPMailer

PHPMailer users may encounter "SSL3_GET_SERVER_CERTIFICATE: certificate verify failed" errors when sending emails from servers with self-signed certificates. This issue arises due to SSL certificate verification introduced in PHP 5.6.

Root Cause:

By default, PHPMailer verifies SSL certificates to ensure their authenticity. When a self-signed certificate is encountered, the verification fails due to the absence of an appropriate CA (Certificate Authority).

Solution:

To resolve this issue, you have two options:

1. Fix SSL Configuration:

If possible, obtain a valid SSL certificate that is signed by a trusted CA and install it correctly on your mail server. This will ensure successful certificate verification.

2. Disable SSL Certificate Verification (Not Recommended):

Warning: Disabling certificate verification has serious security implications. It exposes you to the risk of man-in-the-middle attacks.

To disable certificate verification, set the following PHPMailer options:

<code class="php">$mail->SMTPOptions = array(
    'ssl' => array(
        'verify_peer' => false,
        'verify_peer_name' => false,
        'allow_self_signed' => true
    )
);</code>

Editing the PHPMailer library to disable verification is highly discouraged as it will break upon upgrades.

Security Considerations:

Disabling SSL certificate verification should only be considered as a temporary workaround, not a long-term solution. It is crucial to secure your SSL configuration to prevent potential security breaches.

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