Which of the following is a common protocol used to secure email communications?

The correct answer is based on the context of securing email communications. IMAP, or Internet Message Access Protocol, is indeed commonly used for retrieving emails, but it can also operate over secure connections, such as with TLS/SSL to encrypt the communication channel. This is important for maintaining confidentiality and ensuring that emails are securely transmitted between the email client and the server.

In contrast, the other protocols listed serve different purposes. HTTP is primarily used for web traffic and does not specifically address email communication. FTP, or File Transfer Protocol, is designed for file transfers, not email security. POP3, which stands for Post Office Protocol version 3, is another email retrieval protocol that can be used securely but is less favored in modern applications that require more features and better support for multiple devices. Thus, while POP3 can also be secured, IMAP is more commonly associated with secure access to email communications.