Resolve an explicit UPN to a implicit UNP (user pricipal name) in active directory

Question

Accourding to this; https://msdn.microsoft.com/nl-nl/library/windows/desktop/aa380525%28v=vs.85%29.aspx?f=255&MSPPError=-2147217396

There are two types of UPN's. (User pricipal name)

• implicit UPN
• explicit UPN (defined by the admin)

Is there a way to resolv the explicit UPN to the implicit UPN from a root domain?

I want to do this with system.directoryservices in vb.net, but c# tips are also welcome.

Thanks