httpcontext.current.server.mappath Object reference not set to an instance of an object

Don't use Server.MapPath. It's slow. Use this instead, HttpRuntime.AppDomainAppPath. As long as your web site is running, this property is always available to you.

Then use it like this:

string filePath = Path.Combine(HttpRuntime.AppDomainAppPath, "email/teste.html");

if the code is not running from within a thread is executing a httprequest then HttpContext.Current is null (for example when you method is called via BeginInvoke) - see http://forums.asp.net/t/1131004.aspx/1 .

You can always use HttpRuntime see http://msdn.microsoft.com/en-us/library/system.web.httpruntime.aspx

If there is no HttpContext (e.g. when the method is called via BeginInvoke, as Yahia pointed out), the call to HttpContext.Current.Server.MapPath() must fail. For those scenarios, there's HostingEnvironment.MapPath() in the System.Web.Hosting namespace.

string filePath = HostingEnvironment.MapPath("~/email/teste.html");