SMTP & POP3
Much confusion exists among users as to the meaning of SMTP and POP3.
The terms SMTP and POP3 stand for Simple Mail Transfer Protocol and
Post Office Protocol version 3 respectively. The full names do give a clue
as to what each is used for, but not enough to leave you much wiser.
The good news is that you do not need to know any of the technical
details of either SMTP or POP3, so you can leave that to the programmers.
We will start with an explanation of SMTP. As the name suggests, it is a
protocol for transferring mail, which means that it is a way of getting
mail to the correct mailbox on the correct computer.
You identify the mailbox by the name to the left of the @ sign, and the
correct computer by the host (computer) and domain name (organisation) to
the right of the @ sign.
Your Internet Service Provider (ISP), keeps track of how to get to each domain, and
sends it on its way without you having to worry about it.
The mail jumps from computer to computer on the way to the mailbox
automatically, as the computers make contact with each other.
Once you have a domain name for your organisation, people can send mail to
any user name in that domain, whether they are real users or not. It
is up to the SMTP software at the final destination computer to reject or
accept the user name.
Note that with SMTP, we have the concept of many users mailboxes
residing on a single computer. This fits in well with 'multi user'
computer systems such as Unix, VMS, Windows NT etc., but not so well with
PC users where each user has their own computer.
This is essentially where all the confusion lies.
For an organisation that wants to connect many PC users to the
Internet, you do not want your final destination of incoming SMTP mail to
be any single PC. If this were the case, when the PC made contact with your
Internet provider, ALL the mail would be sucked off onto the PC for ALL
So, what do organisations with separate PC's do?
Basically, you subscribe to a company that has a multi user computer,
who will set up mail accounts on their machine for all your users. So all
mail for your organisation gets sent to their computer, not yours.
So how do your PC users get to see their mail? Well, they use a POP3
mail client which connects to the computer on which the mail resides, and
copies the mail for that user onto the PC .... without using SMTP.
Well what about sending mail out? Well that depends on the software you
are using. Most POP3 clients now use SMTP to send outgoing mail, but that
is no problem, because mail is not being transferred onto the PC. Some
ISPs provide POP3 as the method of users receiving mail,
some provide SMTP, and some provide both. So which type of service should
If you only wish to connect a single user to the Internet, it makes no
real difference whether you subscribe to a POP3 mail service or an SMTP
mail service. The only difference is that with a POP3 mail account,
the sender will usually need to get both the user name and domain name
correct, whereas with an SMTP mail account, the mail will arrive on your
PC whatever the user name. To recap, this is because when receiving mail
using SMTP, you are effectively subscribing your computer, and all mail
destined for that computer, regardless of user will be sent to it. With
POP3 mail, you are paying for a specific mail user name to be set up on
your ISPs computer.
If you wish to connect a few PC users at a site to the Internet, or
have a single nominated PC user at several different locations, you would
be best to opt for POP3 mail accounts. This allows each individual to pick
up their own mail without fetching other peoples mail. However, there will
be a cost for each new user that you ask your ISP to set up
If you wish to provide Internet E-mail accounts for many users who are
networked at a site, or if you are running a multi-user operating system
such as Unix, VMS or Windows NT/2000, you would be better advised to opt for an
SMTP mail connection, and nominate a computer at your site to be a Mail
Server which picks up all mail for your site and organises distribution to
the individual users. If this is the case, your options are many and
varied, and would depend on the mixture of equipment, operating systems
and networks that you have installed.
As a matter of interest, you may not be aware that Windows 2000 Server has a built-in SMTP server. If you would like some information on how to configure it, click here.
Some of the information above has been provided by C2000.