Looking for "SMTP injection" sample code

Howdy, My company has written an php page that gets email addresses from SQL DB, then sends the mails out via the built-in sendmail commands. This is for subscriber based emails, not spam. Formerly we've been using sendmail, but we recently switched to postfix for various reasons, including virtual domain support. However, Postfix runs twice as slow with the mail() function as sendmail does, that's very unacceptable. Poeple on the Postfix mailing list said that this is the result of using the sendmail command line, which is very un-optimized. they said we need to use SMTP port injection for fast mailing. Unfortunately we are very new to php, and don't know how to do this. Does anyone have some sample code showing this method of sending mail via smtp?, that you'd be willing to share? This is on a Red Hat Linux system, by the way. Thanks, JW