Identify the protocol commonly used for sending email.

The Simple Mail Transfer Protocol (SMTP) is the core protocol used for sending email messages across the Internet. SMTP operates over the TCP/IP protocol suite, and it primarily handles the process of sending messages from a sender's mail server to a recipient's mail server. This protocol is responsible for the task of transferring email between different servers, which is essential for the delivery of messages.

SMTP works by establishing a connection between email servers and then using that connection to send email from the sender to the recipient. It can also relay the email through various servers until it reaches its final destination. SMTP utilizes a set of commands and replies to facilitate the communication between the client (sending server) and the server (receiving server), ensuring that the email is delivered reliably.

While protocols like Post Office Protocol (POP) are important for retrieving emails from a mail server and File Transfer Protocol (FTP) is suitable for transferring files, they do not play a role in the email sending process itself. Hypertext Transfer Protocol (HTTP) is primarily used for transferring web pages and does not deal with email functions. Therefore, the significance of SMTP in the context of email communication confirms its status as the standard protocol for sending emails.