In order to make a IMAP connection to a Microsoft Exchange Server 5.5, I used this connection-string :
<?php
if(imap_open ("{192.168.1.6:143/imap}Inbox", "DOMAIN/USERNAME/ALIAS", "PASSWORD"))
{
 echo 'Connection success!';
}
else
{
 echo 'Connection failed';
}
?>

By replacing "Inbox" with, e.g. "Tasks", its possible to see all your tasks. I Hope this helps anybody!
Regards