Which protocol primarily handles sending emails over TCP?

The protocol that primarily handles sending emails over TCP is SMTP, which stands for Simple Mail Transfer Protocol. SMTP is designed specifically for sending email messages from one server to another and is a fundamental part of the email transmission process. When you send an email, it typically travels from your email client to the email server using the SMTP protocol.

SMTP works over the TCP transport layer, ensuring reliable communication. The use of TCP allows SMTP to maintain the integrity of the email data being transmitted, making sure that emails are delivered accurately without loss or corruption. It operates on port 25 by default, though other ports can be used for secure connections, such as port 587 for submissions.

In contrast, other protocols mentioned serve different purposes. HTTP (Hypertext Transfer Protocol) is used primarily for transferring web pages, making it essential for web browsing but not for sending emails. SSH (Secure Shell) is used for secure remote login and command execution, primarily in the context of network device management. DNS (Domain Name System) is responsible for translating domain names into IP addresses, which is crucial for routing traffic on the internet but does not handle email transmission directly. Therefore, SMTP is the correct choice for the protocol that manages sending emails over TCP.