What is the primary function of SMTP, which operates on port 25?

The primary function of SMTP, or Simple Mail Transfer Protocol, is to send mail from a device to a mail server. This protocol is essential for the process of sending outgoing emails, allowing clients, such as email applications or web-based services, to transmit email messages over the internet. When you compose and send an email, SMTP is responsible for transferring that message from your device to the designated mail server, ensuring it reaches its destination.

This functionality is specifically facilitated through communications occurring over port 25, which is the standard port for SMTP. This protocol focuses primarily on the sending and relaying of emails, differentiating it from other protocols that might handle different aspects of email communication.

The other options relate to different functionalities. Receiving emails is typically managed by protocols such as IMAP or POP3, which allow clients to retrieve messages from a mail server. Converting names to IP addresses is the role of DNS, and managing email inboxes involves organizing and storing emails, which is also related to IMAP or POP3 rather than SMTP. Thus, the selected answer correctly identifies the primary function of SMTP in the context of email communication.