What are some alternative methods to mail() for debugging PHP scripts, especially in the context of IPN scripts?

When debugging PHP scripts, especially in the context of IPN scripts where mail() may not be reliable or practical, alternative methods such as error_log(), var_dump(), and using a debugging tool like Xdebug can be helpful. These methods allow for easier tracking of errors and variables in the script without relying on email notifications.

// Using error_log() to log errors or debug information
error_log("An error occurred: " . $error);

// Using var_dump() to output variable values for debugging
var_dump($variable);

// Using Xdebug for more advanced debugging capabilities
// Set breakpoints in your code and step through it to track variables and errors