In the context of PHP programming, what are some common reasons why a previously effective spam protection system may stop working after a server or script upgrade, and how can these issues be resolved?

One common reason why a spam protection system may stop working after a server or script upgrade is due to changes in PHP versions or server configurations that affect how the system interacts with external services or databases. To resolve this issue, you may need to update your code to be compatible with the new PHP version or server settings.

// Example code snippet to update spam protection system for PHP 7.4 compatibility

// Before upgrade
$spam_check_result = check_spam($user_input);

// After upgrade
$spam_check_result = check_spam_updated($user_input);

function check_spam_updated($input) {
    // Updated spam protection logic
}