What port does Simple Mail Transfer Protocol (SMTP) use?

The correct response identifies that the Simple Mail Transfer Protocol (SMTP) primarily operates over port 25. This port is the standard assigned for SMTP, which is used for sending emails between servers and facilitates the transmission of email messages. Additionally, port 587 is also commonly used for SMTP, particularly for mail submission, as it allows for secure transmission via STARTTLS, which encrypts the communication.

Port 110 is associated with Post Office Protocol version 3 (POP3), which is designed for receiving emails from a server, while port 143 is used for Internet Message Access Protocol (IMAP), another protocol for receiving emails. Therefore, while port 587 is indeed related to SMTP, port 25 remains the traditional and widely recognized port for the core SMTP functionality.