The correct answer is Authorization, since authorization is concerned with how access rights are defined and how they are evaluated.

This functionality is provided through mail services, this service permits collaboration between users in an internal and external level. We usually use two protocols, "SMTP" in port TCP 25 to send the emails and "POP3" in port TCP 110 to receive them. Currently there is another protocol that is gaining popularity, it is "IMAP4". Print services are used for printing documents and file services are used to share and access files and folders inside the infrastructure.

The MIME protocol specifies a structure for the body of an email message. MIME supports a number of formats in the email body, including graphic, enhanced text and audio, but does not provide security services for these messages. S/MIME defines such services for MIME as digital signatures and encryption based on a standard syntax. *Answer IPSEC is incorrect since IPSEC is not an email protocol but is a standard that provides encryption, access control, nonrepudiation, and authentication of messages over IP. It is designed to be functionally compatible with IPv6. Answer b is incorrect because PGP, Pretty Good Privacy, brings security to email through the use of a symmetric cipher, such as IDEA, to encipher the message. RSA is used for symmetric key exchange and for digital signatures. PGP is not an augmentation of MIMe. RFC 2440 permits other algorithms to be used in PGP. In order of preference, they are ElGamal and RSAfor key distribution; triple DES, IDEAand CAST5 for encryption of messages; DSA and RSA for digital signatures and SHA-1 or MD5 for generating hashes of the messages. Answer d is incorrect because there is no such protocol. There is a protocol called SET for Secure Electronic Transaction. It was developed by Visa and MasterCard to secure electronic bankcard transactions. SET requests authorization for payment and requires certificates binding a person's public key to their identity.