【User】How to check if a user name belongs to a domain

using System.DirectoryServices.AccountManagement;

...

try
{
var principalContext = new PrincipalContext(ContextType.Domain, domain);

using (
var user = UserPrincipal.FindByIdentity(
principalContext, IdentityType.SamAccountName, account))
{
if (user == null)
{
ModelState.AddModelError("UserName","UserNotExistInAD");
}
}
}
catch (PrincipalServerDownException)
{
ModelState.AddModelError("UserName", "DomainNotExistOrNotAvailable");
}
catch (PrincipalException)
{
ModelState.AddModelError("UserName", "UserNotExistInAD");
}