Email through external PHP/SMTP

**Wanted: The ability to send email from Server A, through a PHP script and/or SMTP server on Server B** I work with a company that has produced a new shopping cart and "follow-up" email autoresponder system with PHP. This is a hosted solution, and will be used by thousands of customers to email their own clients/newsletter subscribers through my servers. However, with so much email going through my system, if one user reports a false spam complaint, it could blacklist my entire IP/network. I would like to create an option inside the site that allows my users to specify an external SMTP server (with user/pass auth) to pass email through their OWN servers when using my software. And, if they don't have SMTP, I would like an alternative PHP that can be installed on their own domain, and my software would then call that script and pass mail to it (which would then email using their own server). Many of the original email headers will need to remain intact. The job includes... - Modifying the existing software to allow a user to enter their SMTP details or the URL to the PHP script (or, select "internal" if they wish for mail to go through our servers) - The PHP script that accepts incoming email data, and sends it internally through its own mail() command (must be stand-alone). - Modifying our own software's mail routines, to either send email through our own server -- or, connect via SMTP/PHP to the specified server settings (for each user). ## Deliverables 1) Work alongside our existing tech team to create a PHP-based solution. 2) Complete ownership of all scripts and all code in each script. 3) All instructions followed and implemented in the code ## Platform PHP 4