Which protocol is commonly used for sending email messages?

The protocol commonly used for sending email messages is SMTP, which stands for Simple Mail Transfer Protocol. SMTP is specifically designed for the exchange of email messages between servers and is the standard protocol utilized when an email is sent from a client (like an email application) to a mail server or between mail servers. It facilitates the transfer of the email content while also handling the routing of messages through various servers until they reach their final destination.

In the context of email, SMTP operates over the TCP/IP protocol suite and typically uses port 25, though it can also operate on other ports such as 587 (for secure email sending). Its capabilities include managing user authentication, queuing messages when the target server is not available, and error reporting, which makes it well-suited for the task of delivering emails.

The other protocols mentioned serve very different purposes. HTTP (Hypertext Transfer Protocol) is primarily used for transferring web pages and other resources over the web, not for sending emails. FTP (File Transfer Protocol) is utilized for the transfer of files between a client and a server, and SNMP (Simple Network Management Protocol) is aimed at network management and monitoring, not email delivery. Consequently, SMTP distinctly stands out as the appropriate protocol for sending email messages.