Complex sentence: The Public Key Name Service is notable because it addresses key deficiencies of hosted communication encryption services which have been criticized because the message remains stored on the providers servers and the problems associated with manually exchanging encryption keys using other encrypted communications technologies like PGP.
Split into simpler sentences: The Public Key Name Service is notable because it addresses key deficiencies of hosted communication encryption services which have been criticized because the message remains stored on the provider's servers. PKNS also alleviates problems associated with manually exchanging encryption keys using other encrypted communications technologies like PGP.