Utilizing the "Mailto" action in this way, you are very limited wrt the format of the information. It is very simple and quite clever but very restrictive.
In this case the browser is calling the user's local email client to formulate (and send) the message.
A more traditional approach is to send the (POST) data to a web server. Using a 'server side' language like PHP, Rails or even CGI you would have complete control over the data.
In addition the delivery of the message would be better assured. (in your current set-up, depending upon the setup of each particular user, there are chances the message is not sent)
You could also capture the data by storing in a database, thereby providing an 'archive' for reference.
With that being said, this is not the place for step-by-step instructions on how to accomplish that. However, with the aid of a book (print or online), many of which are available from Sitepoint, you can be assured direct answers to your questions and problems along the way by [re]visiting this forum.
If this is strictly an 'internal' project you may not have the budget to pay a professional to help you. At the same time you would have the latitude to stumble a bit as you learn. And the education you gain from DIY is invaluable!!