in reply to Saving sent email from LAMP to MS Exchange Folder
First, the quick and cheesy way. Send a receipt to the sender's email, and then have them use a mail filter on their side to simply move it from the Inbox to Sent Items. Simple and effective, but the user would have to have the filter set up.
To really do this, I believe you would need to use a Windows box with Outlook installed. Then use MAPI to send mail from a program on the Windows side. Perl MAPI code example. You will need the user's password for this to work. You could have a service running on Windows that listens for a connection from the LAMP side, and then sends the mail this way.