tFPDF | modified version of FPDF that adds UTF | User Interface library

The max_execution_time is counted from request start to end. It does not reset when calling a new function.

However, reading the documentation over at https://www.php.net/manual/en/info.configuration.php#ini.max-execution-time will tell you

The maximum execution time is not affected by system calls, stream operations etc. Please see the set_time_limit() function for more details.

So I guess your calls out to the mailing service don't count towards the total execution time, hence your script can run for 7-8 minutes before finally hitting the PHP runtime limitation.

So, to circumwent your problem with the script running into timeouts when sending emails, you could either increase the max_execution_time if you have access to the php.ini file or if your PHP Configuration allows ini_set, you can increase the limit manually for this specific script.

Maybe you could even use set_time_limit to increase your maximum runtime every time you've successfully sent out one email.

Another, more complex but also more robust, solution would be to implement some kind of email queue, which is then perpetually processed by a cli script via cron. This way, you don't have to worry about exceeding the script runtime. You could put all information about the mails you need to send into a file, or database table, and your cron script could read those jobs and execute them.