advanced PHP invite script

I need a php script written to allow address book users of Yahoo, gmail, hotmail, msn and aol to retrieve their contact lists directly from an external website (my site). The imported email addresses and/or contact names can be used to send invitation emails and have the option of being stored in the MySQL database. I already have a script like this running on my server but, I want this script to send the invitation email using the person's ISP's server (Yahoo servers, gmail servers, etc..) instead of sending the invite using my dedicated server. It should take the login info they enter on my site and login to their email, retrieve their address book and they then select who they wish to invite (all contacts should be selected by default) and then when they click send invitation, it logs into their email in the background and sends the invitation via their email provider's servers. This script will need updates regularly and I'm willing to pay to keep it updated.