What are common configuration errors related to sendmail and SMTP that can affect PHP mail functionality?

Common configuration errors related to sendmail and SMTP that can affect PHP mail functionality include incorrect sendmail_path configuration in php.ini, misconfigured SMTP server settings, and firewall blocking outgoing SMTP connections. To solve these issues, ensure that the sendmail_path in php.ini is correctly set to the path of the sendmail binary, verify that the SMTP server settings in the PHP mail function are accurate, and check if any firewall rules are blocking outgoing SMTP connections.

// Example PHP code snippet to set the correct sendmail_path in php.ini
ini_set('sendmail_path', '/usr/sbin/sendmail -t -i');