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Resolving PHP Deprecation Warnings in Post SMTP

33 threads Sep 16, 2025

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If you've recently upgraded your server's PHP version, you might have noticed a flood of deprecation warnings from the Post SMTP plugin appearing in your error logs. This is a common experience for many users moving to PHP 8.1 or higher. This guide will explain why these warnings occur and what you can do about them.

Understanding PHP Deprecation Warnings

Deprecation warnings are not errors. They are messages from PHP indicating that the code is using features that will be removed in a future version of PHP. The functionality of the Post SMTP plugin remains intact; emails will continue to send. However, these warnings can clutter your debug logs, making it difficult to spot genuine, critical errors.

Common Post SMTP Deprecation Warnings

Based on community reports, the most frequent warnings include:

  • Implicit conversion from float NAN to int: Occurs in PostmanUtils.php on lines ~215-222.
  • Passing null to parameter of type string: Often found in PostmanEmailAddress.php and the bundled Zend library files when a function like trim() receives a null value.
  • Dynamic property creation: Seen in classes like Postman_Zend_Mail_Protocol_Smtp_Auth_Crammd5 where properties are created on the fly without declaration.
  • Return type compatibility: Warnings related to the ArrayAccess interface in the Freemius SDK and the old Zend library.
  • Array to string conversion: Triggered when an array is passed to a function expecting a string, such as a script version number in PostmanSuggestProSocket.php.

Why This Happens

The core of the issue lies in the plugin's code and its bundled libraries (namely an old version of the Zend framework and the Freemius SDK). These components were written for older PHP versions that had different standards. PHP 8.1 and later enforce stricter type checking and coding standards, leading to these deprecation notices.

Solutions and Workarounds

1. Wait for an Official Plugin Update

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 is actively aware of these issues. As seen in the support threads, they have acknowledged the warnings and often state that fixes are planned for upcoming releases. Keeping your plugin updated is the best long-term solution.

2. Adjust Your Debugging Settings (Recommended Short-Term Fix)

Since these are non-critical warnings, the simplest solution is to configure your wp-config.php file to suppress deprecation notices while keeping other error reporting active.

// Disable display of all error types on the live site
ini_set('display_errors', 0);

// You can also suppress specific deprecation errors if needed
// ini_set('error_reporting', E_ALL & ~E_DEPRECATED);

This prevents the warnings from breaking page layout (e.g., the "headers already sent" error) and clogging your logs, while still allowing major errors to be reported if logged elsewhere.

3. Roll Back Your PHP Version (Not Recommended)

If the warnings are causing significant development overhead and you cannot adjust logging, temporarily rolling back to PHP 8.0 or 7.4 will eliminate them. However, this is a backward step for security and performance. This should only be considered a very temporary measure until a plugin update is available.

Conclusion

PHP deprecation warnings in Post SMTP are a known side effect of progress in the PHP language. They signal that the plugin's code needs to be modernized, but they do not impact its core email-sending functionality. The most practical approach is to manage your error reporting settings to ignore these specific warnings while waiting for the plugin developers to release a fully compatible update.

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