Get current user's email address in .NET

Reference System.DirectoryServices.AccountManagement, then

using System.DirectoryServices.AccountManagement;
return UserPrincipal.Current.EmailAddress;

See .NET docs UserPrincipal.Current and UserPrincipal.EmailAddress.

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Or with a timeout:

var task = Task.Run(() => UserPrincipal.Current.EmailAddress);
if (task.Wait(TimeSpan.FromSeconds(1)))
    return task.Result;
    

If you're behind a Windows domain, you could always grab their email address out of Active Directory.

See Javier G. Lozano's example in his tutorial, "Querying Active Directory for User Emails".