Network Protocols Glossary
What is a network protocol? Protocols are the rules of the road for how data exists and moves on the network. They allow many different systems and computers to communicate.
Simple Mail Transfer Protocol (SMTP)
What is Simple Mail Transfer Protocol (SMTP)?
SMTP is used to send and receive email. It is sometimes paired with IMAP or POP3 (for example, by a user-level application), which handles the retrieval of messages, while SMTP primarily sends messages to a server for forwarding. SMTP can both send and receive mail, but it's bad at queuing incoming messages, hence the common delegation to other protocols. Proprietary systems like Gmail have their own mail transfer protocols when using their own servers, but they still use good old SMTP to email beyond that.
What is the purpose of SMTP
SMTP is an asymmetrical protocol, meaning that there are many clients interacting with one server, using a basic model popular in the 1980s which is now mostly defunct outside of email protocols. SMTP runs on TCP/IP and listens on port 25.