If you receive “500 server-side error” from save_email.php in the browser network tab log then at first check your apache log for specified error. If error any of these…
Handler for (null) returned invalid result code 70007
For apache error related to timeout, mod_proxy, mod_fcgi_proxy fix – you can simply comment or remove this line from apache httpd.conf file
LoadModule reqtimeout_module modules/mod_reqtimeout.so
Also, it is best not to use any proxy or timeout configurations apache module with this script. As it will make you do a lot of unnecessary settings adjustments to run the script properly in background.
Then most likely file size is big and you have to increase your max_allowed_packet to 16M or higher value based on your server memory.
Check MySQL server has gone away after install complete! for more details on this configuration.