Create a page (or a dialog box, I prefer using jQuery UI but I'm going to do this example as a page cuz I'm lazy)
To: <asp:TextBox runat="server id="To_TB /><br />
Subject: <asp:TextBox runat="server" id="Subject_TB" /><br />
Body:<br />
<asp:TextBox runat="server" id="Body_TB" TextMode="Multiline" /
<br />
<asp:Button runat="server" id="Submit_BTN" Text="Send Email" OnClick="Submit_BTN_Click" />
Codebehind...
protected void Submit_BTN_Click(object sender, EventArgs e)
{
MailMessage msg=new MailMessage("myserver@mysite.com", To_TB.Text, Subject_TB.Text, Body_TB.Text);
SmtpClient client=new SmtpClient("myemailserver@mydomain.com");
client.Send(msg);
}
It can obviously me much fancier, HTML emails and MailAddress instead of strings and all that jazz. But this should get you started. You'll have full control over it, unlike depending on the user having an email client.