Please try based on this code :
<%@ Page Language="C#" Title="First sample" %>
<%@ Import Namespace="CuteWebUI" %>
<%@ Register TagPrefix="CuteWebUI" Namespace="CuteWebUI" Assembly="CuteWebUI.AjaxUploader" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd">
<script runat="server">
protected void Button1_Click(object sender, EventArgs e)
{
System.Web.Mail.MailMessage msg = new System.Web.Mail.MailMessage();
msg.From = "mymail@myhost.com";
msg.To = "yourmail@yourmail.com";
msg.Subject = "Test";
msg.Body = "Test";
foreach (AttachmentItem item in UploadAttachments1.Items)
{
if (!item.Checked) continue;
//string filename = item.FileName;
//int filesize=item.FileSize;
//Stream stream=item.OpenStream();
System.Web.Mail.MailAttachment ma
= new System.Web.Mail.MailAttachment(item.GetTempFilePath());
msg.Attachments.Add(ma);
}
System.Web.Mail.SmtpMail.Send(msg);
}
</script>
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
</head>
<body>
<form id="Form1" runat="server">
<CuteWebUI:UploadAttachments runat="server" ID="UploadAttachments1" InsertText="UploadAttachments1">
</CuteWebUI:UploadAttachments>
<br />
<asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="Send" Width="107px" />
</form>
</body>
</html>