as you can see, this post is being so complicated and seems -almost-nobody have time to read it in details to solve the problem, so i will just manimize the issue as follow:
our emails sending on the current server is only 150 emails per hour. once cron is executed is doesn't send anything as obviously there is more than that in the queue so it crashes and sending errors to the firstname.lastname@example.org which i put as default noreply email address.
cron is sending each 15 minutes as default by moodle and it is working fine.
1- how i can modify this to make the emails being out less than 150 emails per hour? for example 25 emails for this cron job or any other idea not to exceed this limit but having most important notifications working as emails...
2- how to make sure that everything before this moemnt are not to be sent, as, with each cron it include everyting from the start and obviously it crashes with our email sending hourly limit...