Email Alerts on saved searches, procedure and safety/performance tips&tricks?

[thongdee]

I built an email alert for my users (now are only 2,000)so every night a crontab execute a php script that query the mysql to find matches with user's saved search. it's a classified website in my case, but i would like to learn in case i had to build something for bigger clientsmy concerns are: [*]what happen if my user grow x10 orx100 times? is the server going tocrash? there any tip you can suggeston manage something like that?[*]there is any way to protect my filecron/nightly_script.php to beexecuted form outside calling it inthe url of the browser? considertham im using a string in crontablike:lynx [absolute url/script.php][*]what about the email blast? for eachquery if the query has results thescript sends an email, so it means ablast of emails...is it going to beconsidered spam automatically andthen i could blacklisted?thanks!!!