Through a blog entry by Urs Gehrig I came to a nice little PHP script, the so-called libgmailer. This little class provides easy access to the Gmail interface through PHP. It supports all necessary methods to send and receive emails, to browse folders and manage contacts. Since everyone has a Gmail account now and most of the people I know do not really use it, libgmailer is a funny way to maybe get some benefit out of Gmail.
Finally after trying, I asked the Author to provide the class into PEAR (which is currently not possible, because of it's license), but maybe that works sometimes.