Which of the following protocols does NOT provide encrypted communications?

The rationale behind identifying SMTP as the protocol that does not inherently provide encrypted communications lies in the typical operations of email transmission. SMTP, or Simple Mail Transfer Protocol, is primarily used for sending emails. By default, SMTP does not incorporate encryption; communications can be sent in plain text, making it vulnerable to interception.

While it is true that SMTP can be secured with the use of additional layers, such as STARTTLS, this encryption is not inherent to the protocol and must be specifically configured to be used. In contrast, the other protocols listed—HTTPS, IMAP, and POP—are designed to include or can be easily secured with encryption. HTTPS is the secure version of HTTP providing encryption for web traffic, IMAP can be secured through IMAPS (IMAP over SSL/TLS), and POP can also utilize POP3S (POP over SSL/TLS) for encrypted communications.

Thus, while various methods exist to secure SMTP, its standard operation lacks the built-in encryption that characterizes the other protocols mentioned. This distinction is why SMTP is the correct answer in this question regarding protocols that do not provide encrypted communications by default.