PHP Mass emailing

Question

I work for a small marketing company that has asked me to develop a PHP application to send emails for their company without getting blacklisted or emails showing up as spam

Answer 1

well, you may simply use mail() but no amount of PHP is going to help you get past spam filters. They use blacklists, statistical filters, human-filters, neural networks and all kinds of technologies to determine if someone is sending spam. 1.000.000 emails per month sounds like spam to me, so most likely you'll be tagged as "spammer" :)