This overload requires the license key be already set (such as with MailBee.Global.LicenseKey property, app.config, web.config, or in Windows registry).

If your application is multi-threaded and you need to have multiple impersonated threads, each such thread must maintain its own instance of Impersonation class. Single-threaded applications need only a single instance of this class.

To get the name of the user account being used by the current thread, call System.Security.Principal.WindowsIdentity.GetCurrent().Name.

Reference