Which protocol is primarily used for sending email?

The protocol primarily used for sending email is Simple Mail Transfer Protocol (SMTP). SMTP is designed specifically for the transmission of emails between mail servers and from email clients to mail servers. It operates over port 25 by default and is a key component of email functionality on the internet.

SMTP facilitates the process of sending and relaying messages, ensuring that emails are directed to the correct recipient's mail server. Its operation involves transferring the email content along with headers that contain various metadata about the email, such as the sender's and recipient's addresses.

In contrast, the other protocols listed serve different purposes: FTP (File Transfer Protocol) is used for transferring files over the internet; HTTP (Hypertext Transfer Protocol) is utilized for accessing web pages; and DNS (Domain Name System) is responsible for translating domain names into IP addresses. Each protocol plays a vital role in networking but does not function in the same capacity as SMTP regarding email transmission.