The cgiemail script is a popular tool which allows visitors to send Email messages to authorized addresses from a Web based form. cgiemail is easy to set up and customize for your particular needs.
Copy the cgiemail directory from /usr/local/share/contrib/ to the cgi-bin of the domain you want to use the script for and change the ownership of the files to the correct user. This must be done as root from the VPS v2 command prompt.
You will need to create a form for the visitors to view. For help creating a form, see The cgiemail example page.
You can find documentation on configuring and using cgiemail from the following site.