Exchange 2010 SP1 and SharePoint 2010 | ExchangeService.AutodiscoverURL(userEmailID) not working

Hi All,

I am in the phase of Project deployment, I am facing an issue in client environment. 

I have created visual web part in which I am using below code to send mail it is working fine in my development environment,

ExchangeService exchangeService = new ExchangeService(ExchangeVersion.Exchange2010_SP1);

exchangeService.AutodiscoverUrl(SPContext.Current.Web.CurrentUser.Email);

exchangeService.UseDefaultCredentials = true;

but it is throwing exception at the point auotdiscoverURL(). I have also tried to pass static URL, but it fails at the point of user authentication and throwing Error 401 .

Please suggest if any one face this issue before.

Thanks in advance.

Praveen