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Troubleshooting Common Post SMTP Plugin PHP Version Compatibility Errors

23 threads Sep 9, 2025

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Many WordPress users rely on the Post SMTP plugin for reliable email delivery. However, a frequent source of problems arises from compatibility issues with different PHP versions. This guide will help you identify and resolve the most common PHP-related errors encountered with the Post SMTP plugin.

Understanding the Core Issue

The Post SMTP plugin has historically had specific compatibility requirements with PHP. Errors often occur when the plugin version is not designed to work with the PHP version running on your server. This can manifest as fatal errors during activation, on the settings page, or when viewing email logs.

Common PHP Version Errors and Their Solutions

1. Activation Errors (SQL Syntax, TypeError, Fatal Error)

Error Examples:

  • PHP Fatal error: Uncaught mysqli_sql_exception: You have an error in your SQL syntax...
  • Fatal error: Uncaught TypeError: array_merge(): Argument #1 must be of type array, string given in .../PostmanInstaller.php:44
  • Plugin could not be activated because it triggered a fatal error.

Solution: These errors often indicate a fundamental incompatibility. The most effective first step is to ensure you are running a recent, updated version of the Post SMTP plugin, as many older activation bugs have been fixed in subsequent releases.

2. PHP 8.0+ Compatibility: Implode() TypeError

Error Example:

  • Uncaught TypeError: implode(): Argument #2 ($array) must be of type ?array, string given in .../PostmanLogFields.php:63

Why it happens: PHP 8.0 introduced stricter type checking for functions like implode(). Code that worked under PHP 7.x may fail if it passes an incorrect data type.

Solution: This specific issue has been addressed in newer versions of the plugin. Updating to the latest available version is the primary solution. If the error persists, temporarily downgrading to PHP 7.4 may be necessary while awaiting a full fix.

3. PHP 8.2+ Compatibility: Dynamic Properties Deprecation

Error Example:

  • Errors related to accessing properties that are not explicitly declared in a class.

Why it happens: PHP 8.2 deprecated the ability to create dynamic properties on objects that weren't defined in the class, which can cause fatal errors.

Solution: One user-reported workaround for a specific class was to explicitly declare the property. For the class PostmanGetDiagnosticsViaAjax, adding public $cleanDiagnostics; inside the class definition resolved their issue. However, such code changes should only be considered if you are comfortable editing plugin files and understand that they may be overwritten by updates. The definitive solution is an official plugin update that includes these declarations.

4. Missing PHP Extensions (GD, gzuncompress)

Error Examples:

  • Uncaught Error: Call to undefined function ImageCreate() in .../qrimage.php:74
  • Uncaught Error: Call to undefined function gzuncompress() in .../qrspec.php:550

Why it happens: These functions are part of the GD (for image processing) and Zlib (for compression) PHP extensions. Some hosting environments, especially on newer PHP versions, may not have these extensions installed or enabled by default.

Solution: Contact your web hosting provider and request that they enable the GD and Zlib extensions for your PHP installation.

5. Class Name Conflicts

Error Example:

  • PHP Fatal error: Cannot declare class qrstr, because the name is already in use in .../qrconst.php on line 50

Why it happens: This occurs when another plugin (e.g., a PDF builder) uses the same third-party library (like phpQRcode) and loads its classes first, causing a conflict when Post SMTP tries to load the same class names.

Solution: This requires a code change from the Post SMTP team to check if a class already exists before declaring it. Users experiencing this should note that 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' team has indicated that fixes for such conflicts have been implemented in beta versions and are scheduled for public release.

General Troubleshooting Steps

  1. Check Your PHP Version: Navigate to Tools > Site Health > Info in your WordPress admin dashboard and look under the Server section to confirm your PHP version.
  2. Update the Plugin: Always ensure you are running the latest version of the Post SMTP plugin, as updates frequently contain compatibility patches for newer PHP versions.
  3. Review the Error Log: Enable WordPress debugging to get detailed error messages, which are essential for diagnosing the specific problem.
  4. Check PHP Extensions: Verify that required extensions like OpenSSL, GD, and Zlib are active on your server. Your hosting provider's control panel or support team can assist with this.
  5. Temporary Downgrade (if possible): If your site is critically broken and you need immediate stability, temporarily reverting to PHP 7.4 can be a workaround while you seek a permanent solution for PHP 8+ compatibility.

By methodically working through these common errors and solutions, you can resolve most PHP version conflicts with the Post SMTP plugin and restore reliable email functionality to your WordPress site.

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