Can I use JavaScript to create a client side email?

What we used in a projet is a popup window that opens a mailto: link, it is the only way we found to compose a mail within the default mail client that works with all mail clients (at least all our clients used).

var addresses = "";//between the speech mark goes the receptient. Seperate addresses with a ;var body = ""//write the message text between the speech marks or put a variable in the place of the speech marksvar subject = ""//between the speech marks goes the subject of the messagevar href = "mailto:" + addresses + "?"         + "subject=" + subject + "&"         + "body=" + body;var wndMail;wndMail = window.open(href, "_blank", "scrollbars=yes,resizable=yes,width=10,height=10");if(wndMail){    wndMail.close();    }

You more or less only have two alternatives when sending mail via the browser..

1. make a page that takes user input, and allows them to send the mail via your web-server. You need some kind of server-side scripting for this.
2. use a mailto: link to trigger opening of the users registered mail client. This has the obvious pitfalls you mentioned, and is less flexible. It needs less work though.

With javascript alone, it's not possible.
Javascript is not intended to do such things and is severely crippled in the way it can interact with anything other than the webbrowser it lives in, (for good reason!).

Think about it: a spammer writing a website with client side javascript which will automatically mail to thousands of random email addresses. If people should go to that site they would all be participating in a distributed mass mailing scam, with their own computer... no infection or user interaction needed!