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Troubleshooting Common Post SMTP Plugin Errors: From Connection Issues to Memory Exhaustion

29 threads Sep 9, 2025

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Users of the 'Post SMTP – WP SMTP Plugin with Email Logs and Mobile App for Failure Notifications – Gmail SMTP, Office 365, Brevo, Mailgun, Amazon SES and more' plugin occasionally encounter errors that can prevent emails from sending or cause issues on their WordPress sites. Based on community support threads, this guide outlines the most common problems and their solutions.

1. cURL and SSL Certificate Errors

Common Error Messages:

  • "cURL error 60: SSL certificate problem: unable to get local issuer certificate"
  • "cURL error 0: The cURL request was retried 3 times and did not succeed"
  • "GuzzleHttp requires cURL, the allow_url_fopen ini setting, or a custom HTTP handler"

Why It Happens: These errors are typically related to server configuration, not the plugin itself. They indicate that the server's PHP installation cannot make secure outbound connections. This can be due to missing CA certificates, an outdated cURL library, or a server-level firewall/security restriction.

Solutions:

  • Contact Your Hosting Provider: This is the most common solution. Ask them to verify that the server's cURL and OpenSSL libraries are up-to-date and that the correct Certificate Authority (CA) bundle is installed and configured.
  • Server Reboot: In some cases, a simple server reboot can resolve temporary connection glitches, as mentioned in one thread.
  • Check PHP Version: Ensure you are using a supported, stable version of PHP. Some users reported issues after switching to PHP 7.3, which were resolved by ensuring proper server configuration for that version.

2. Memory Exhaustion and Fatal Errors

Common Error Messages:

  • "Fatal error: Allowed memory size of XXXXXX bytes exhausted"
  • Critical error when viewing the Email Log page

Why It Happens: This occurs almost exclusively on sites with very large email logs (thousands of entries). The Email Log page tries to load a vast amount of data from the database into memory, exceeding PHP's memory limit. The data is stored in the standard WordPress `wp_postmeta` table.

Solutions:

  • Increase PHP Memory Limit: Temporarily increase the memory limit in your `wp-config.php` file (define('WP_MEMORY_LIMIT', '512M');). This is a workaround, not a permanent fix.
  • Purge Old Email Logs: This is the most effective solution. To prevent the log from growing too large, regularly navigate to Post SMTP → Email Log and delete old entries. For bulk deletion, you may need to run a direct SQL query on your database to remove records from the `wp_postmeta` table where the `meta_key` is like '%post_smtp%', but caution is advised as this should only be done by someone comfortable with database management.
  • Database Optimization: After purging logs, use a database optimization plugin to clean up and reduce the overall table size.

3. Transaction and API Errors (e.g., Amazon SES, Gmail)

Common Error Messages:

  • "554 Transaction failed: Unsupported encoding 'UTF-8'"
  • "554 Transaction failed: Expected parameter value, got """
  • "Bad Request(invalid_grant)" with Gmail

Why It Happens: These are service-specific errors passed through from your SMTP provider (e.g., Amazon SES, Gmail) to the plugin. They can be caused by incorrect configuration, authentication issues, or changes on the provider's end.

Solutions:

  • Re-authenticate: For OAuth services like Gmail, try disconnecting and re-authenticating the connection. This often clears stale tokens.
  • Verify SMTP Settings: Double-check all credentials, region settings (for SES), and from-email addresses against your provider's documentation. Ensure the "Envelope From" email matches the account used for authentication.
  • Check Provider Status: Occasionally, the issue may be a temporary outage or API change on the provider's end.

4. Form Submission Conflicts (e.g., Elementor, CF7)

Common Error Messages:

  • "parserror" in AJAX response
  • Form freezes or returns a server error (500)

Why It Happens: This is usually a plugin conflict where the email-sending process interferes with the form plugin's AJAX response, often related to how the from name/address is handled.

Solutions:

  • Toggle "Prevent Changes" Setting: In the Post SMTP settings (Message tab), try checking the "Prevent plugins and themes from changing this" box for both the sender name and address. This can prevent conflicts with other plugins trying to filter the email headers.
  • Plugin Conflict Test: Deactivate all other plugins except Post SMTP and your form builder. If the problem resolves, reactivate plugins one by one to identify the culprit.

General Troubleshooting Tip: The Diagnostic Report

When asking for help in community forums, you will often be asked for the Post SMTP Diagnostic Report. This is the first step in troubleshooting. You can find it by navigating to Post SMTP → Settings → Diagnostic. This report provides essential information about your server's configuration that is vital for diagnosing problems.

Remember, many errors related to cURL, SSL, and memory are rooted in server environment configuration. Working closely with your hosting provider is often the fastest path to a resolution.

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