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POP and SMTP

After your e-mail client knows your e-mail address, it's going to need to know where to look for
incoming e-mail and where to send outgoing e-mail.
Your incoming e-mails are going to be on a computer called a POP server. The POP server –
usually named something like pop.smallnetwork.net or mail.smallnetwork.net – has a file on it
that is associated with your e-mail address and which contains e-mails that have been sent to
you from someone else. POP stands for post office protocol.
Your outgoing e-mails will be sent to a computer called a SMTP server. This server – named
smtp.smallnetwork.net – will look at the domain name contained in the e-mail address of any
e-mails that you send, then will perform a DNS lookup to determine which POP3 server it
should send the e-mail to. SMTP stands for simple mail transfer protocol.
When you start up your e-mail client, a number of things happen:
1. the client opens up a network connection to the POP server
2. the client sends your secret password to the POP server
3. the POP server sends your incoming e-mail to your local computer
4. the client sends your outgoing e-mail to the SMTP server.
The first thing to note is that you do not send a password to the SMTP server. SMTP is an old
protocol, designed in the early days of e-mail, at a time when almost everyone on the
Internet knew each other personally. The protocol was written with the assumption that
everyone who would be using it would be trustworthy, so SMTP doesn't check to ensure that
you are you. Most SMTP servers use other methods to authenticate users, but – in theory –
anyone can use any SMTP server to send e-mail

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