This option is available only when a certificate is associated with the POP3 virtual server. To encrypt all information transmitted across the network, you must require that a secure channel be used. When private messages are sent, Exchange ensures that the body of a message is encrypted from the moment it leaves the source until the moment it is read by the recipient.
Tip Exchange uses 40-bit encryption by default. To strengthen encryption, you can require that the largest key possible be created. Using 128-bit encryption creates a larger key, which is more difficult for unauthorized users to guess.
To require encryption: