What is the standard port number for Simple Mail Transfer Protocol (SMTP) used to send email?

The standard port number for Simple Mail Transfer Protocol (SMTP), which is responsible for sending email, is 25. This protocol is primarily used for transferring email messages between servers and is essential for the sending process in email communication. The use of port 25 has been a long-standing convention in network communications, and it is designated for SMTP traffic, allowing for the reliable sending of emails from client applications to mail servers or between mail servers.

Understanding the function of SMTP is crucial, as it contrasts with those ports associated with other services. For instance, port 110 is used for Post Office Protocol version 3 (POP3), which is a protocol for receiving emails, while port 53 handles Domain Name System (DNS) queries. Additionally, port 443 is utilized for secure HTTP traffic, also known as HTTPS, focusing on web security and data transmission rather than email handling.

This distinction among different service protocols and their associated port numbers is key in network configuration and security, which is essential knowledge for individuals studying information security fundamentals.