Knowledge on how email works?
If you are interested to know how messages are delivered and sent, how
mail servers contact each other, and how users retrieve their
email. This will help you, and knowing who to contact (or
blame!) when something goes wrong. The information in this
section is not specific to one or other mail server or service
providers. This is written purely educational purpose. In the
process of writing an email, sending and receiving, viewing an
email there are mainly two components involve and they are
“Email Client” and “Email Server”
What
is an Email Client?
An
email client is a software application that is used to send,
receive, store and view an e-mail.
Some examples of email
clients are:
- Microsoft Outlook
- Microsoft Outlook Express
- Thunderbird
- AOL Mail
- Lotus Notes
Sometimes
you may also use your browser as a mail client. For example you
can access your Gmail, Hotmail and Yahoo accounts using your web
browser such as Internet Explorer, FireFox or Google Chrome
What
is an Email Server?
An
email server holds and distributes e-mail messages for email
clients. A
mail / email server (AKA a mail transfer agent or MTA, a mail
transport agent, a mail router or an Internet
mailer or a mail
exchange server)
is an application that receives incoming e-mail from people
within the same domain & remote senders and forwards
outgoing e-mail for delivery to respective recipient. A computer
dedicated to running such applications is also called a mail
server.
The email client connects to
the email server and retrieves messages. There are many
email servers are available in the market that you can buy. Microsoft Exchange
Server, q-mail, Exim, MailEnable, MDeamon and Sendmail are some
of the many mail server programs.
Transporting
the Email (Sending & Receiving)
To
send Internet e-mail, requires an Internet connection and access
to a mail server. The standard protocol (set of rules or a
program on your computer) used for sending Internet e-mail is
called SMTP (Simple Mail Transfer Protocol). The SMTP
protocol is used to both send and receive email
messages over the Internet.
When a message is sent, the email client sends the message to
the mail server using Simple Mail Transfer Protocol. If
the recipient of the email is local (i.e. in same domain as the
email originated from) the message is kept on the server for
accessing by the POP (stands for Post Office Protocol), IMAP
(stands for Internet Mail Access Protocol)
or other mail services for later retrieval. This is a mail
protocol that enables emails to be retrieved from a remote
mailbox. Often both SMTP and POP services would be running from
the same server (or computer). However, in some cases, one
server is used for receiving mail (AKA POP server) and another
server is used for sending mail (AKA SMTP server).
If
the recipient is remote (i.e. at another domain), the mail
server communicates with a Domain Name Server (DNS) (of the
remote domain) to find the corresponding IP address for the
domain being sent to. Once the IP address has been
resolved, the SMTP server connects with the remote SMTP server
and the mail is delivered to this server for handling.
If the mail server sending
the mail is unable to connect with the remote mail server, then
the message goes into a queue. Messages in this queue will
be retried periodically. If the message is still
undelivered after a certain amount of time (let us say 30 hours
by default), the message will be returned to the sender as
undelivered.