Site içinde kullandığım E-mail uygulamasının kodları...

//css
#dvFrame
{
   width: 600px;
   margin: 0 auto;
   padding: 5px;
   text-align: left;
   border: solid 1px gray;
   background-color: White;
}
#lblHead
{
   clear: left;
   color: #495a92;
   float: left;
   font-size: 15px;
   font-weight: bold;
   text-decoration: none;
}
#imgSPRT
{
   height: 1px;
   width: 99%;
   padding-top: 5px;
   padding-bottom: 10px;
}
#btnSend
{
   margin-left: 120px;
   margin-top: 5px;
   width: 90px;
   border: solid 1px #c0c0c0;
   font-size: 12px;
}
#valSum
{
   font-size: 12px;
   color: Maroon;
}
#lblWarning
{
   text-align: center;
   width: 100%;
   font-size: 12px;
   color: Maroon;
}
.mailLabel
{
   float: left;
   width: 120px;
   font-weight: bold;
   font-size: 12px;
}
.mailText
{
   width: 180px;
   margin-bottom: 5px;
   border: solid 1px #c0c0c0;
   font-size: 12px;
}
.mailDesc
{
   width: 350px;
   height: 150px;
   border: solid 1px #c0c0c0;
   font-size: 12px;
}

//aspx
<div id="dvFrame">
<asp:Label ID="lblHead" runat="server" Text="E-mail" /><br />
<img id="imgSPRT" src="images/bar.gif" alt="sprt" />
<asp:Label ID="lblName" runat="server" CssClass="mailLabel" Text="Ad" />
<asp:TextBox ID="txtName" runat="server" CssClass="mailText" />
<asp:RequiredFieldValidator ID="rqrName" runat="server" ControlToValidate="txtName"
Display="None" ErrorMessage="Ad Gerekli." ValidationGroup="mail" /><br />
<asp:Label ID="lblMail" runat="server" CssClass="mailLabel" Text="E-mail" />
<asp:TextBox ID="txtMail" runat="server" CssClass="mailText" />
<asp:RequiredFieldValidator ID="rqrMail" runat="server" ControlToValidate="txtMail"
Display="None" ErrorMessage="E-mail Gerekli." ValidationGroup="mail" />
<asp:RegularExpressionValidator ID="rqeMail" runat="server" ControlToValidate="txtMail"
Display="None" ErrorMessage="Geçersiz E-mail." ValidationExpression="\w+([-+.']\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*" ValidationGroup="mail" /><br />
<asp:Label ID="lblMessage" runat="server" CssClass="mailLabel" Text="Mesaj" />
<asp:TextBox ID="txtMessage" runat="server" CssClass="mailDesc" TextMode="MultiLine" />
<asp:RequiredFieldValidator ID="rqrMessage" runat="server" ControlToValidate="txtMessage"
Display="None" ErrorMessage="Mesaj Gerekli." ValidationGroup="mail" /><br />
<asp:Button ID="btnSend" runat="server" Text="Gönder" OnClick="btnSend_Click" ValidationGroup="mail" /><br />
<asp:ValidationSummary ID="valSum" runat="server" ValidationGroup="mail" /><br />
<asp:Label ID="lblWarning" runat="server"></asp:Label>
</div>

//cs
StringBuilder messageBody = new StringBuilder();
messageBody.Append("Name : ");
messageBody.Append(txtName.Text.Trim());
messageBody.Append("\n");
messageBody.Append("Email : ");
messageBody.Append(txtMail.Text.Trim());
messageBody.Append("\n");
messageBody.Append("Message : ");
messageBody.Append(txtMessage.Text.Trim());
messageBody.Append("\n");
//from ile To aynı adres olabilir.
MailMessage newMessage = new MailMessage("from@mailserver.com", "to@mailserver.com", "Contact", messageBody.ToString());
SmtpClient newSmtp = new SmtpClient("mail.mailserver.com");
newSmtp.Credentials = new System.Net.NetworkCredential("from@mailserver.com", "password");
try
{
   newSmtp.Send(newMessage);
   lblWarning.Text = "Tamam, Mesajınız bana iletildi...";
}
catch
{
   lblWarning.Text = "Hata, tekrar deneyin.";
}