Simple Mail Transfer Protocol

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SMTP is a simple text-based protocol for tranferring mail (email) messages. It works best between machines that are permanently connected (to the internet).

By convention, SMTP uses TCP port 25 for communication.

By Example

As SMTP is just a simple text-based protocol, we can use a simple text communication client like Telnet to talk to an SMTP server. For example:

telnet mail.it.swin.edu.au 25

Example Output More information is coming on this topic...

SMTP & Relay Hosts

There is no user authentication built in to SMTP. As a result the development of SPAM prevention methods has become a major issue for ISP who offer email services to clients.

Servers that do not restrict the sending of email from clients are open to exploitation as a "relay host" -- anyone can send email through that SMTP server.

A good methods for SMTP servers is to not allow connections from hosts that are not in a white list of allowed hosts. For example, students at Swinburne can connect to a university SMTP server and send email while connected to the university network (and allocated a university IP number). However if the same student was connected to their own ISP at home (with the ISP's IP number), they would not be allow to use the university SMTP server to send email because they are not in the "white list" of allowed university IP numbers.

For retrieving email POP3 is commonly used, although a newer IMAP has several advantages.

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