I'm going to be designing a script to check a MySQL database nightly (via a cronjob) to find users who meet certain criteria. It will then need to notify that person via a short email. This is going to be a fairly large system and it will need to probably email around ~1000ish people an night. (Disclaimer: NO, this is not spam and is on an opt-in basis) Have any of you accomplished a mailer script on a large scale? What do I need to focus on to ensure scalability and reliability? Oh, and I'm planning to write this in PHP.