Which protocol is commonly used for sending emails?

Simple Mail Transfer Protocol (SMTP) is the standard protocol used for sending emails across the Internet. It is designed specifically for the transmission of email messages between servers, which makes it essential in the email delivery process. When a user sends an email from their email client, SMTP is the protocol that communicates with the email server to initiate the sending process and direct the email to the recipient's mail server.

Email communication relies on a set of protocols, and while there are other protocols involved in retrieving and storing emails (such as IMAP or POP3), SMTP is the one used for sending. This focused function is what establishes SMTP as a crucial component in the electronic mail ecosystem.

The other protocols listed serve different purposes: Internet Control Message Protocol (ICMP) is generally used for network diagnostics and management; File Transfer Protocol (FTP) is utilized for transferring files between networked computers; and Dynamic Host Configuration Protocol (DHCP) is responsible for assigning IP addresses to devices on a network. Each of these protocols has a specific function that does not overlap with the primary purpose of email transmission.