过滤高容量数据库,然后向这些数据库发送大量电子邮件

I have a database with 20k people in it. How can I safely filter through it and then sending an email to those that correspond to my criteria? Let's say my filter returns 5k emails

I was thinking to add a parameter to database; let's say status and update it to 1, and then to rewrite the .htaccess to create a cron job that runs a script only for those that have status set to 1 from 10 to 10 mins with limit 100 and update status to 0 again. Any of you have a better idea? or is my idea bad?

I'm using PHPmailer.