Like a lawyer never asking a question whose (correct) answer is not yet known, there are emails that have the "fingerprints" of that server. Thus, if an imposter-server were offered in place of the true server, it would be quickly recognized as not containing the known fingerprint and having passed the known-to-have-been-shipped-through-the-original-server email. In such a case, the penalities on Ms Rodham would mount even higher and implicate even more people, as Ms Rodham ain't no techie do be able to do such things by herself.
HF