C# razor MVC4

I have a requirement in MVC4 with razor to send mail to a person.I have added view with tosend,mesage,subject and file with two button add file and send.as;

<pre lang="c#"><form >
<table>
<tr>
<td>
@html.Textboxfor(m=m.Files)
</td>
</tr>
<tr>
 <td>
    <input type="submit" name="Add File">
</td>
</tr>
</table>

I have also made model mailmodel as

public string tosend
{get;set;}

public string Subject
{
get;
set;
}
public string files
{
get;set;
}

I have save all the entry to database but how can i dynamically add more control for files when Add file is clicked and option to browse for file.I am new to it pleasae help