Messaging is older than the web services and in some ways easier to provide. In this section, I'm first going to look at the elder statesman of messaging services: e-mail.
Nowadays, we also use systems that send SMS textual information and we will look at two of these: Twitter and Esendex.
Sending e-mails conventionally happens on the well-known port 25, although other ports such as 465 and 587 are now more commonly used (http://www.esendex.co.uk).
This uses the Simple Mail Transport Protocol (SMTP), which was first formulated in the early 1980s and consists of formulating a message the SMTP server can understand, with fields such as To:, From:, and Subject: together with the text of the message and then deposit in the mail service's outbound queue.
Receiving emails is a little different. This depends on one of the different protocols such as the Post Office Protocol (POP) or alternatively the Internet Message Access Protocol (IMAP). Each has its own related set of ports, and...
