Sam, a web developer, was instructed to incorporate a hybrid encryption software program into a web application to secure email messages. Sam used an encryption software, which is a free implementation of the OpenPGP standard that uses both symmetric-key cryptography and asymmetric-key cryptography for improved speed and secure key exchange.
What is the encryption software employed by Sam for securing the email messages?

A. PGP
B. SMTP
C. GPG
D. S/MIME