How to Fix WordPress Error: Subsite SMTP Settings Not Working

When managing a WordPress multisite network, you might encounter issues with subsite SMTP settings not functioning correctly. Despite correctly entering the mailserver_url, mailserver_login, mailserver_pass, and mailserver_port in the settings, transactional emails might still fail to send from the subsite. Interestingly, installing an SMTP plugin on the subsite and using the same information can resolve the issue. This article will explore potential causes and solutions for this problem.

Understanding the Issue

The problem at hand involves correctly entered SMTP settings not working within a WordPress subsite, but functioning correctly when an SMTP plugin is used. Several factors could contribute to this discrepancy:

1. SMTP Configuration Conflict: The multisite setup might have overriding configurations that affect subsites.

2. Server Restrictions: The hosting environment might impose restrictions on email sending directly from the WordPress application.

3. Plugin Conflicts: Other plugins installed on the network or subsite might interfere with the SMTP settings.

4. WordPress Core Settings: The core WordPress email handling might not be properly configured for multisite environments.

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Steps to Diagnose and Fix the Issue

1. Verify Multisite Configuration

First, ensure that your multisite network is correctly configured to handle email sending. This includes verifying the following:

• Network Admin Settings: Check the network admin settings to ensure there are no conflicting email configurations.
• Subsite-Specific Settings: Confirm that the subsite settings for SMTP are correctly entered and saved.

2. Check Hosting Environment

Some hosting providers have specific restrictions or configurations that can affect SMTP settings. Verify with your hosting provider if there are any known issues or restrictions regarding sending emails from subdomains or subsites. Additionally, ensure that the mailserver credentials are correct and that the mail server is reachable from your hosting environment.

3. Install and Configure an SMTP Plugin

Given that the SMTP plugin works, it indicates that the issue might be related to how WordPress handles SMTP settings natively. Install a reliable SMTP plugin like WP Mail SMTP or Easy WP SMTP on the subsite and configure it with the same SMTP credentials. This can often bypass any native WordPress limitations or conflicts.

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4. Check for Plugin Conflicts

Other plugins on your network might interfere with SMTP settings. To identify potential conflicts:

• Deactivate Plugins: Temporarily deactivate all plugins on the subsite and network to see if the issue persists. If the emails start sending, reactivate plugins one by one to identify the culprit.
• Review Plugin Settings: Some plugins, especially security or optimization plugins, might have settings that block or modify email sending. Review their configurations.

5. Review WordPress Core Settings

WordPress core settings for handling emails might not be optimized for a multisite environment. To address this:

• Custom Code: Consider adding custom code to your wp-config.php file or your theme’s functions.php file to handle SMTP settings explicitly. For example:

add_action('phpmailer_init', 'configure_smtp');
function configure_smtp(PHPMailer $phpmailer) {
    $phpmailer->isSMTP();
    $phpmailer->Host = 'your_mailserver_url';
    $phpmailer->SMTPAuth = true;
    $phpmailer->Port = 587; // or your_mailserver_port
    $phpmailer->Username = 'your_mailserver_login';
    $phpmailer->Password = 'your_mailserver_pass';
    $phpmailer->SMTPSecure = 'tls'; // or 'ssl' if required
    $phpmailer->From = 'your_email@example.com';
    $phpmailer->FromName = 'Your Name or Site Name';
}

6. Check DNS and Email Authentication

Ensure that your domain’s DNS settings are correctly configured for email delivery. This includes setting up SPF, DKIM, and DMARC records. These settings help authenticate your emails and improve deliverability, reducing the likelihood of emails being blocked or marked as spam.

7. Contact Support

If all else fails, contacting WordPress support forums or your hosting provider’s support team can provide additional insights or solutions specific to your setup.

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Conclusion

Fixing SMTP issues in a WordPress multisite environment can be challenging due to the complexity of configurations and potential conflicts. By systematically verifying settings, using reliable SMTP plugins, checking for conflicts, and configuring email authentication, you can address and resolve the issue effectively. If needed, don’t hesitate to seek help from support channels to ensure your subsite’s transactional emails are sent successfully.