SMTP stands for simple mail transfer protocol and is the protocol used for
sending email on the Internet.
The SMTP protocol is use by your email client to send email to the email server
of you email provider and is also used when email servers send email to each
other.
To help in understanding the SMTP email process
it is useful to compare the sending and receiving of email with the sending and
receiving of normal postal mail.
To send normal mail you simply go to any post box and drop in your letter. To
send email on the Internet you connect your email to any SMTP server and send
your email.
The SMTP server can belong to anyone and doesn't need to be the same
as your normal email provider.
This was the case until the system was abused and innocent ISPs were used for
sending SPAM.
Today almost all SMTP servers only allow you to send email through
them if you are using either a trusted IP address (one they themselves
allocated) or you must first authenticate yourself (login).
SMTP Authentication
There are three ways email providers authenticate an SMTP user.
IP address- Not configurable in client
Authentication via login -Configurable in client
Sender email address--Configurable in client
IP address
When you connect to your ISP you are allocated and IP address. If your email
account is held by your ISP then you normally don't need to authenticate to send
email. This is because the ISP detects that the sending SMTP client has a known
IP address and hence trusts it.
Accessing Your email Using a different IP address than Normal
This scenario is typical when you have a dial up or broadband account and you
are able to send email normally from home but when you visit another office and
connect to their Network you find that you are able to receive email ok but not
send email.
This is because the email provider as detected that you are using an IP address
that is not trusted and hence thinks you are trying to spam. The usual solution
is to configure SMTP authentication as detailed below.
Login or SMTP Authentication
If your ISP isn't your email provider then you normally need to login in order
to send email. This is configured in Outlook Express as detailed below:
From the Tools menu, choose
Accounts.
Select the Mail tab.
Click the account to highlight it.
Click the properties button
Select the Servers tab.
Check the box next to My Server Requires
Authentication.
Usually you logon using the same account as for POP3 email. If
so then you have finished configuration. However you may be sending
mail using a different provider than for receiving email. This
happens often when moving ISPs. If this is the case you will need to
click settings tab and then select the logon using
radio button and enter a username and password.
Click OK.
Sender Email Address
When sending email some email servers will check that the address
in the from field is a registered email address on that sever. If
you have an email account on that server then it isn't a problem
provided that you have entered your details correctly in the client
configuration.
However if you are using you client to access multiple email
addresses/accounts and are trying to send all email through a single
SMTP server then this may cause problems. Some email providers
recognise this and allow you to enter other addresses that you may
use in the send field. They usually have a mechanism to verify that
the address belongs to you.
An ISP (internet service provider) provides physical dialup or broadband
connection to the Internet. ISP also generally provide other web services like
email accounts and web space. e.g.. BT, Cable and Wireless.
A Web portal doesn't provide Internet access but Internet services like email,
web hosting e.g. Yahoo. To use these you need first to connect to the Internet
using an ISP.