Final answer:
For email security on an open network, enable SSL (Secure Sockets Layer) to encrypt the communication between your email client and server.
Step-by-step explanation:
When using an open network, it is crucial to ensure that your email configuration includes SSL (Secure Sockets Layer) enabled. SSL is a security protocol that encrypts information between your email client and the email server, providing security by ensuring that any sensitive data sent over the network is not easily accessible to hackers and eavesdroppers. Options such as POP (Post Office Protocol), SMTP (Simple Mail Transfer Protocol), and IMAP (Internet Message Access Protocol) relate to how emails are received and sent but do not pertain directly to securing your email data over an open network.