Simple Mail Transfer Protocol

Simple Mail Transfer Protocol (SMTP)

SImple Mail Transfer Protocol is an internet protocol designed to send and receive e-mail messages between e-mail servers over the Internet.

 

 

SMTP was developed to send e-mail messages across the Internet. In the OSI model, SMPT is an application layer protocol that utilizes TCP as the transport protocol to transmit mail to a destination mail exchanger, in other words, SMTP is used to transmit mail to a mail server. Mail can be transmitted by a client to the mail exchanger server, or from mail exchanger to mail exchanger. Mail sent via SMTP is usually sent from one mail exchanger to another, directly. E-mail was never designed to be instantaneous, but that is often how it appears to us.

Mail Exchangers are the name given to the applications that support the SMTP protocol. Mail Exchangers such as sendmail or Microsoft Exchange should listen for IP datagrams that arrive on the network interface with a TCP port number of 25. This port is one of the 'well known ports' defined in RFC 1700. When a message is received, the mail exchanger should check to see if it is for one of it's users, then move the mail to the user's mailbox.

Simple mail transfer protocol differs from Post Office Protocol version 3 (POP3). POP3 is used by e-mail client applications such as Microsoft Outlook, Mozilla Thunderbird, Eudora and other e-mail applications to retreive mail stored in personal mailboxes at the mail server.