SMTP (Simple Mail Transfer Protocol) is a standard protocol used for sending and relaying email messages between email clients and email servers over a TCP/IP network such as the internet. SMTP defines a set of commands and rules for routing, delivering, and relaying email messages between mail transfer agents (MTAs) and mail delivery agents (MDAs). SMTP servers use port 25 or other designated ports for listening to incoming email connections and forwarding outgoing email messages to their destinations.
