Till 1971, people were able to send messages to other people working on same system only. In 1971, the first e-mail message was sent by Ray Tomlinson. Though that was a very simple message based communication but it formed the basis of how advanced e-mails have become today.
The main components of an e-mail system that facilitate sending and receiving of e-mails on Internet are:
Let’s study these and then finally try to connect the dots to understand the complete system.
An Email Client
If you use e-mails for online communication then you would definitely be using an e-mail client. An e-mail client provides you with the following capabilities:
The e-mail clients could be standalone (like Microsoft Outlook, Pegasus etc) or could be web based (like Gmail, yahoo etc). There could be many advanced abilities that e-mail clients may provide but whatever the type of e-mail client be, the core abilities described above are provided by all type of clients.
Whenever you send a message from your e-mail client, it goes to an e-mail server. The e-mail server manages the messages received by it. It forwards the message to a POP or IMAP service if the message is to be sent to a recipient on the same subnet else it follows the standard procedure to send the message over Internet to the destined person.
An e-mail server comes into the picture twice if e-mail is sent over Internet to a remote destination. First it’s the sender’s e-mail server that sends the e-mail over the Internet and second is the receiver’s e-mail server that receives the e-mail and makes sure that it is delivered to the recipient’s system. On the other hand, an E-mail server comes into picture only once when the recipient is on the same subnet.
SMTP servers are widely used as e-mail servers all over the internet. An SMTP server is also known as Mail Transfer Agent (MTA).
As already explained, these servers come into the picture when a message is received by SMTP server and it needs to be forwarded to the actual recipient. Let’s discuss both these servers one by one:
POP stands for Post Office Protocol. A POP (or POP3) server in its simplest form stores the messages for a particular user in a text file. The file for a particular user is appended with information each time an e-mail is received by a POP server. If your e-mail client is configured to use a POP3 protocol then whenever you try to fetch e-mails through your e-mail client then a request is sent to your POP server for the same.
A POP server requires the log-in credentials of a user that are sent through e-mail client. Once a user is authenticated, the POP server provides access to user’s e-mails. As with any client server architecture, the e-mail client interacts with the POP server through a predefined set of commands.
Here is a list of common commands used to interact with POP server:
Please note that the e-mail client connects to port 110 on the server where POP service is running. After connecting the e-mail client issues the commands (as described above) to the POP server to authenticate, fetch e-mail, list e-mails etc.
IMAP stands for Internet message access protocol. This protocol is also used to access e-mails but it is far more capable than POP. One of the most prominent features an IMAP server provides is the central access to e-mails. Unlike POP server, an IMAP server keeps the e-mails on the server itself and so you can access e-mails from any machine or device.
This server also provides easy management of e-mails like searching, categorizing the e-mails and placing them into various sub-folders etc. The only problem that one could imagine with IMAP server is that you always need an Internet connection so that the e-mail client is able to fetch e-mails from the IMAP server. But today, almost all of the e-mail clients have the capability to cache the e-mails so that you can even view them when you are offline.
To interact with IMAP server, the e-mail client connects to server machine on port 143. As with POP, IMAP server also understands a set of commands which the e-mail client uses to connect with the server.
Connecting the Dots
With the understanding of all the major components used in e-mail system, lets connect the dots and understand how the whole e-mail system works:
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