Modern e-mail clients support this method allowing users to receive various types of files as attachments to e-mail messages.

(GPG)

S/MIME supports encryption and the use of in e-mail.

(MDA)

An alternative to S/MIME is a method developed by Philip Zimmerman for encrypting and decrypting e-mail messages.

(MTA)

PGP uses this encryption system.

(MUA)

When the recipient receives the message, he or she decrypts it with his or her .

(PDA)